- 07 May, 2007 40 commits
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Benjamin Herrenschmidt authored
Generic hugetlb_get_unmapped_area() now handles MAP_FIXED by just calling prepare_hugepage_range() Signed-off-by:
Benjamin Herrenschmidt <benh@kernel.crashing.org> Acked-by:
William Irwin <bill.irwin@oracle.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Cc: David Howells <dhowells@redhat.com> Cc: Andi Kleen <ak@suse.de> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Kyle McMartin <kyle@mcmartin.ca> Cc: Grant Grundler <grundler@parisc-linux.org> Cc: Matthew Wilcox <willy@debian.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Adam Litke <agl@us.ibm.com> Cc: David Gibson <david@gibson.dropbear.id.au> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in x86_64 arch_get_unmapped_area(), simple case, just return the address as passed in Signed-off-by:
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in hugetlb_get_unmapped_area on sparc64 by just using prepare_hugepage_range() Signed-off-by:
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in parisc arch_get_unmapped_area(), just return the address. We might want to also check for possible cache aliasing issues now that we get called in that case (like ARM or MIPS), leave a comment for the maintainers to pick up. Signed-off-by:
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in ia64 arch_get_unmapped_area and hugetlb_get_unmapped_area(), just call prepare_hugepage_range in the later and is_hugepage_only_range() in the former. Signed-off-by:
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in i386 hugetlb_get_unmapped_area(), just call prepare_hugepage_range. Signed-off-by:
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in arch_get_unmapped_area on frv. Trivial case, just return the address. Signed-off-by:
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Benjamin Herrenschmidt authored
ARM already had a case for MAP_FIXED in arch_get_unmapped_area() though it was not called before. Fix the comment to reflect that it will now be called. Signed-off-by:
Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by:
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Benjamin Herrenschmidt authored
Handle MAP_FIXED in alpha's arch_get_unmapped_area(), simple case, just return the address as passed in Signed-off-by:
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Benjamin Herrenschmidt authored
The current get_unmapped_area code calls the f_ops->get_unmapped_area or the arch one (via the mm) only when MAP_FIXED is not passed. That makes it impossible for archs to impose proper constraints on regions of the virtual address space. To work around that, get_unmapped_area() then calls some hugetlbfs specific hacks. This cause several problems, among others: - It makes it impossible for a driver or filesystem to do the same thing that hugetlbfs does (for example, to allow a driver to use larger page sizes to map external hardware) if that requires applying a constraint on the addresses (constraining that mapping in certain regions and other mappings out of those regions). - Some archs like arm, mips, sparc, sparc64, sh and sh64 already want MAP_FIXED to be passed down in order to deal with aliasing issues. The code is there to handle it... but is never called. This series of patches moves the logic to handle MAP_FIXED down to the various arch/driver get_unmapped_area() implementations, and then changes the generic code to always call them. The hugetlbfs hacks then disappear from the generic code. Since I need to do some special 64K pages mappings for SPEs on cell, I need to work around the first problem at least. I have further patches thus implementing a "slices" layer that handles multiple page sizes through slices of the address space for use by hugetlbfs, the SPE code, and possibly others, but it requires that serie of patches first/ There is still a potential (but not practical) issue due to the fact that filesystems/drivers implemeting g_u_a will effectively bypass all arch checks. This is not an issue in practice as the only filesystems/drivers using that hook are doing so for arch specific purposes in the first place. There is also a problem with mremap that will completely bypass all arch checks. I'll try to address that separately, I'm not 100% certain yet how, possibly by making it not work when the vma has a file whose f_ops has a get_unmapped_area callback, and by making it use is_hugepage_only_range() before expanding into a new area. Also, I want to turn is_hugepage_only_range() into a more generic is_normal_page_range() as that's really what it will end up meaning when used in stack grow, brk grow and mremap. None of the above "issues" however are introduced by this patch, they are already there, so I think the patch can go ini for 2.6.22. This patch: Handle MAP_FIXED in powerpc's arch_get_unmapped_area() in all 3 implementations of it. Signed-off-by:
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David Rientjes authored
Fixes a deadlock in the OOM killer for allocations that are not __GFP_HARDWALL. Before the OOM killer checks for the allocation constraint, it takes callback_mutex. constrained_alloc() iterates through each zone in the allocation zonelist and calls cpuset_zone_allowed_softwall() to determine whether an allocation for gfp_mask is possible. If a zone's node is not in the OOM-triggering task's mems_allowed, it is not exiting, and we did not fail on a __GFP_HARDWALL allocation, cpuset_zone_allowed_softwall() attempts to take callback_mutex to check the nearest exclusive ancestor of current's cpuset. This results in deadlock. We now take callback_mutex after iterating through the zonelist since we don't need it yet. Cc: Andi Kleen <ak@suse.de> Cc: Nick Piggin <npiggin@suse.de> Cc: Christoph Lameter <clameter@engr.sgi.com> Cc: Martin J. Bligh <mbligh@mbligh.org> Signed-off-by:
David Rientjes <rientjes@google.com> Cc: <stable@kernel.org> Signed-off-by:
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Yasunori Goto authored
The current panic_on_oom may not work if there is a process using cpusets/mempolicy, because other nodes' memory may remain. But some people want failover by panic ASAP even if they are used. This patch makes new setting for its request. This is tested on my ia64 box which has 3 nodes. Signed-off-by:
Yasunori Goto <y-goto@jp.fujitsu.com> Signed-off-by:
Benjamin LaHaise <bcrl@kvack.org> Cc: Christoph Lameter <clameter@sgi.com> Cc: Paul Jackson <pj@sgi.com> Cc: Ethan Solomita <solo@google.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by:
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Akinobu Mita authored
Currently failslab injects failures into ____cache_alloc(). But with enabling CONFIG_NUMA it's not enough to let actual slab allocator functions (kmalloc, kmem_cache_alloc, ...) return NULL. This patch moves fault injection hook inside of __cache_alloc() and __cache_alloc_node(). These are lower call path than ____cache_alloc() and enable to inject faulures to slab allocators with CONFIG_NUMA. Acked-by:
Pekka Enberg <penberg@cs.helsinki.fi> Signed-off-by:
Akinobu Mita <akinobu.mita@gmail.com> Cc: Christoph Lameter <clameter@sgi.com> Signed-off-by:
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Christoph Lameter authored
It is not necessary to tell the slab allocators to align to a cacheline if an explicit alignment was already specified. It is rather confusing to specify multiple alignments. Make sure that the call sites only use one form of alignment. Signed-off-by:
Christoph Lameter <clameter@sgi.com> Signed-off-by:
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Christoph Lameter authored
This patch provides a new macro KMEM_CACHE(<struct>, <flags>) to simplify slab creation. KMEM_CACHE creates a slab with the name of the struct, with the size of the struct and with the alignment of the struct. Additional slab flags may be specified if necessary. Example struct test_slab { int a,b,c; struct list_head; } __cacheline_aligned_in_smp; test_slab_cache = KMEM_CACHE(test_slab, SLAB_PANIC) will create a new slab named "test_slab" of the size sizeof(struct test_slab) and aligned to the alignment of test slab. If it fails then we panic. Signed-off-by: -
Christoph Lameter authored
This patch was recently posted to lkml and acked by Pekka. The flag SLAB_MUST_HWCACHE_ALIGN is 1. Never checked by SLAB at all. 2. A duplicate of SLAB_HWCACHE_ALIGN for SLUB 3. Fulfills the role of SLAB_HWCACHE_ALIGN for SLOB. The only remaining use is in sparc64 and ppc64 and their use there reflects some earlier role that the slab flag once may have had. If its specified then SLAB_HWCACHE_ALIGN is also specified. The flag is confusing, inconsistent and has no purpose. Remove it. Acked-by:
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Peter Zijlstra authored
invalidate_bdev() is superfluous when truncate_inode_pages() is also called. do call invalidate_bh_lrus() though, to avoid stale pointers. Signed-off-by:
Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by:
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Peter Zijlstra authored
Remove duplicate work in kill_bdev(). It currently invalidates and then truncates the bdev's mapping. invalidate_mapping_pages() will opportunistically remove pages from the mapping. And truncate_inode_pages() will forcefully remove all pages. The only thing truncate doesn't do is flush the bh lrus. So do that explicitly. This avoids (very unlikely) but possible invalid lookup results if the same bdev is quickly re-issued. It also will prevent extreme kernel latencies which are observed when blockdevs which have a large amount of pagecache are unmounted, by avoiding invalidate_mapping_pages() on that path. invalidate_mapping_pages() has no cond_resched (it can be called under spinlock), whereas truncate_inode_pages() has one. [akpm@linux-foundation.org: restore nrpages==0 optimisation] Signed-off-by:
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Peter Zijlstra authored
Remove the destroy_dirty_buffers argument from invalidate_bdev(), it hasn't been used in 6 years (so akpm says). find * -name \*.[ch] | xargs grep -l invalidate_bdev | while read file; do quilt add $file; sed -ie 's/invalidate_bdev(\([^,]*\),[^)]*)/invalidate_bdev(\1)/g' $file; done Signed-off-by:
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Nick Piggin authored
Avoid down_write of the mmap_sem in madvise when we can help it. Acked-by:
Hugh Dickins <hugh@veritas.com> Signed-off-by:
Nick Piggin <npiggin@suse.de> Cc: Rik van Riel <riel@redhat.com> Signed-off-by:
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matze authored
Signed-off-by:
Matthias Kaehlcke <matthias.kaehlcke@gmail.com> Signed-off-by:
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Akinobu Mita authored
kmem_cache_create() for slob doesn't handle SLAB_PANIC. Signed-off-by:
Matt Mackall <mpm@selenic.com> Signed-off-by:
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David Miller authored
I ported this to sparc64 as per the patch below, tested on UP SunBlade1500 and 24 cpu Niagara T1000. Signed-off-by:
David S. Miller <davem@davemloft.net> Signed-off-by:
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Christoph Lameter authored
On x86_64 this cuts allocation overhead for page table pages down to a fraction (kernel compile / editing load. TSC based measurement of times spend in each function): no quicklist pte_alloc 1569048 4.3s(401ns/2.7us/179.7us) pmd_alloc 780988 2.1s(337ns/2.7us/86.1us) pud_alloc 780072 2.2s(424ns/2.8us/300.6us) pgd_alloc 260022 1s(920ns/4us/263.1us) quicklist: pte_alloc 452436 573.4ms(8ns/1.3us/121.1us) pmd_alloc 196204 174.5ms(7ns/889ns/46.1us) pud_alloc 195688 172.4ms(7ns/881ns/151.3us) pgd_alloc 65228 9.8ms(8ns/150ns/6.1us) pgd allocations are the most complex and there we see the most dramatic improvement (may be we can cut down the amount of pgds cached somewhat?). But even the pte allocations still see a doubling of performance. 1. Proven code from the IA64 arch. The method used here has been fine tuned for years and is NUMA aware. It is based on the knowledge that accesses to page table pages are sparse in nature. Taking a page off the freelists instead of allocating a zeroed pages allows a reduction of number of cachelines touched in addition to getting rid of the slab overhead. So performance improves. This is particularly useful if pgds contain standard mappings. We can save on the teardown and setup of such a page if we have some on the quicklists. This includes avoiding lists operations that are otherwise necessary on alloc and free to track pgds. 2. Light weight alternative to use slab to manage page size pages Slab overhead is significant and even page allocator use is pretty heavy weight. The use of a per cpu quicklist means that we touch only two cachelines for an allocation. There is no need to access the page_struct (unless arch code needs to fiddle around with it). So the fast past just means bringing in one cacheline at the beginning of the page. That same cacheline may then be used to store the page table entry. Or a second cacheline may be used if the page table entry is not in the first cacheline of the page. The current code will zero the page which means touching 32 cachelines (assuming 128 byte). We get down from 32 to 2 cachelines in the fast path. 3. x86_64 gets lightweight page table page management. This will allow x86_64 arch code to faster repopulate pgds and other page table entries. The list operations for pgds are reduced in the same way as for i386 to the point where a pgd is allocated from the page allocator and when it is freed back to the page allocator. A pgd can pass through the quicklists without having to be reinitialized. 64 Consolidation of code from multiple arches So far arches have their own implementation of quicklist management. This patch moves that feature into the core allowing an easier maintenance and consistent management of quicklists. Page table pages have the characteristics that they are typically zero or in a known state when they are freed. This is usually the exactly same state as needed after allocation. So it makes sense to build a list of freed page table pages and then consume the pages already in use first. Those pages have already been initialized correctly (thus no need to zero them) and are likely already cached in such a way that the MMU can use them most effectively. Page table pages are used in a sparse way so zeroing them on allocation is not too useful. Such an implementation already exits for ia64. Howver, that implementation did not support constructors and destructors as needed by i386 / x86_64. It also only supported a single quicklist. The implementation here has constructor and destructor support as well as the ability for an arch to specify how many quicklists are needed. Quicklists are defined by an arch defining CONFIG_QUICKLIST. If more than one quicklist is necessary then we can define NR_QUICK for additional lists. F.e. i386 needs two and thus has config NR_QUICK int default 2 If an arch has requested quicklist support then pages can be allocated from the quicklist (or from the page allocator if the quicklist is empty) via: quicklist_alloc(<quicklist-nr>, <gfpflags>, <constructor>) Page table pages can be freed using: quicklist_free(<quicklist-nr>, <destructor>, <page>) Pages must have a definite state after allocation and before they are freed. If no constructor is specified then pages will be zeroed on allocation and must be zeroed before they are freed. If a constructor is used then the constructor will establish a definite page state. F.e. the i386 and x86_64 pgd constructors establish certain mappings. Constructors and destructors can also be used to track the pages. i386 and x86_64 use a list of pgds in order to be able to dynamically update standard mappings. Signed-off-by:
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Christoph Lameter authored
Add the tool which gets reports about slabs to the VM documentation directory. Signed-off-by:
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Christoph Lameter authored
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Christoph Lameter authored
Make sure that the check function really only check things and do not perform activities. Extract the tracing and object seeding out of the two check functions and place them into slab_alloc and slab_free Signed-off-by:
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Christoph Lameter authored
At kmem_cache_shrink check if we have any empty slabs on the partial if so then remove them. Also--as an anti-fragmentation measure--sort the partial slabs so that the most fully allocated ones come first and the least allocated last. The next allocations may fill up the nearly full slabs. Having the least allocated slabs last gives them the maximum chance that their remaining objects may be freed. Thus we can hopefully minimize the partial slabs. I think this is the best one can do in terms antifragmentation measures. Real defragmentation (meaning moving objects out of slabs with the least free objects to those that are almost full) can be implemted by reverse scanning through the list produced here but that would mean that we need to provide a callback at slab cache creation that allows the deletion or moving of an object. This will involve slab API changes, so defer for now. Cc: Mel Gorman <mel@skynet.ie> Signed-off-by:
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Christoph Lameter authored
This patch enables listing the callers who allocated or freed objects in a cache. For example to list the allocators for kmalloc-128 do cat /sys/slab/kmalloc-128/alloc_calls 7 sn_io_slot_fixup+0x40/0x700 7 sn_io_slot_fixup+0x80/0x700 9 sn_bus_fixup+0xe0/0x380 6 param_sysfs_setup+0xf0/0x280 276 percpu_populate+0xf0/0x1a0 19 __register_chrdev_region+0x30/0x360 8 expand_files+0x2e0/0x6e0 1 sys_epoll_create+0x60/0x200 1 __mounts_open+0x140/0x2c0 65 kmem_alloc+0x110/0x280 3 alloc_disk_node+0xe0/0x200 33 as_get_io_context+0x90/0x280 74 kobject_kset_add_dir+0x40/0x140 12 pci_create_bus+0x2a0/0x5c0 1 acpi_ev_create_gpe_block+0x120/0x9e0 41 con_insert_unipair+0x100/0x1c0 1 uart_open+0x1c0/0xba0 1 dma_pool_create+0xe0/0x340 2 neigh_table_init_no_netlink+0x260/0x4c0 6 neigh_parms_alloc+0x30/0x200 1 netlink_kernel_create+0x130/0x320 5 fz_hash_alloc+0x50/0xe0 2 sn_common_hubdev_init+0xd0/0x6e0 28 kernel_param_sysfs_setup+0x30/0x180 72 process_zones+0x70/0x2e0 cat /sys/slab/kmalloc-128/free_calls 558 <not-available> 3 sn_io_slot_fixup+0x600/0x700 84 free_fdtable_rcu+0x120/0x260 2 seq_release+0x40/0x60 6 kmem_free+0x70/0xc0 24 free_as_io_context+0x20/0x200 1 acpi_get_object_info+0x3a0/0x3e0 1 acpi_add_single_object+0xcf0/0x1e40 2 con_release_unimap+0x80/0x140 1 free+0x20/0x40 SLAB_STORE_USER must be enabled for a slab cache by either booting with "slab_debug" or enabling user tracking specifically for the slab of interest. Signed-off-by: -
Christoph Lameter authored
We leave a mininum of partial slabs on nodes when we search for partial slabs on other node. Define a constant for that value. Then modify slub to keep MIN_PARTIAL slabs around. This avoids bad situations where a function frees the last object in a slab (which results in the page being returned to the page allocator) only to then allocate one again (which requires getting a page back from the page allocator if the partial list was empty). Keeping a couple of slabs on the partial list reduces overhead. Empty slabs are added to the end of the partial list to insure that partially allocated slabs are consumed first (defragmentation). Signed-off-by:
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Christoph Lameter authored
This enables validation of slab. Validation means that all objects are checked to see if there are redzone violations, if padding has been overwritten or any pointers have been corrupted. Also checks the consistency of slab counters. Validation enables the detection of metadata corruption without the kernel having to execute code that actually uses (allocs/frees) and object. It allows one to make sure that the slab metainformation and the guard values around an object have not been compromised. A single slabcache can be checked by writing a 1 to the "validate" file. i.e. echo 1 >/sys/slab/kmalloc-128/validate or use the slabinfo tool to check all slabs slabinfo -v Error messages will show up in the syslog. Note that validation can only reach slabs that are on a list. This means that we are usually restricted to partial slabs and active slabs unless SLAB_STORE_USER is active which will build a full slab list and allows validation of slabs that are fully in use. Booting with "slub_debug" set will enable SLAB_STORE_USER and then full diagnostic are available. Note that we attempt to push cpu slabs back to the lists when we start the check. If the cpu slab is reactivated before we get to it (another processor grabs it before we get to it) then it cannot be checked. Signed-off-by:
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Christoph Lameter authored
If slab tracking is on then build a list of full slabs so that we can verify the integrity of all slabs and are also able to built list of alloc/free callers. Signed-off-by:
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Christoph Lameter authored
Object tracking did not work the right way for several call chains. Fix this up by adding a new parameter to slub_alloc and slub_free that specifies the caller address explicitly. Signed-off-by:
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Christoph Lameter authored
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Christoph Lameter authored
The patch adds PageTail(page) and PageHead(page) to check if a page is the head or the tail of a compound page. This is done by masking the two bits describing the state of a compound page and then comparing them. So one comparision and a branch instead of two bit checks and two branches. Signed-off-by:
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Christoph Lameter authored
If we add a new flag so that we can distinguish between the first page and the tail pages then we can avoid to use page->private in the first page. page->private == page for the first page, so there is no real information in there. Freeing up page->private makes the use of compound pages more transparent. They become more usable like real pages. Right now we have to be careful f.e. if we are going beyond PAGE_SIZE allocations in the slab on i386 because we can then no longer use the private field. This is one of the issues that cause us not to support debugging for page size slabs in SLAB. Having page->private available for SLUB would allow more meta information in the page struct. I can probably avoid the 16 bit ints that I have in there right now. Also if page->private is available then a compound page may be equipped with buffer heads. This may free up the way for filesystems to support larger blocks than page size. We add PageTail as an alias of PageReclaim. Compound pages cannot currently be reclaimed. Because of the alias one needs to check PageCompound first. The RFC for the this approach was discussed at http://marc.info/?t=117574302800001&r=1&w=2 [nacc@us.ibm.com: fix hugetlbfs] Signed-off-by:
Nishanth Aravamudan <nacc@us.ibm.com> Signed-off-by:
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Christoph Lameter authored
PowerPC uses the slab allocator to manage the lowest level of the page table. In high cpu configurations we also use the page struct to split the page table lock. Disallow the selection of SLUB for that case. Signed-off-by:
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Christoph Lameter authored
Makes SLUB behave like SLAB in this area to avoid issues.... Throw a stack dump to alert people. At some point the behavior should be switched back. NULL is no memory as far as I can tell and if the use asked for 0 bytes then he need to get no memory. Signed-off-by:
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Christoph Lameter authored
Structures may contain u64 items on 32 bit platforms that are only able to address 64 bit items on 64 bit boundaries. Change the mininum alignment of slabs to conform to those expectations. ARCH_KMALLOC_MINALIGN must be changed for good since a variety of structure are mixed in the general slabs. ARCH_SLAB_MINALIGN is changed because currently there is no consistent specification of object alignment. We may have that in the future when the KMEM_CACHE and related macros are used to generate slabs. These pass the alignment of the structure generated by the compiler to the slab. With KMEM_CACHE etc we could align structures that do not contain 64 bit values to 32 bit boundaries potentially saving some memory. Signed-off-by:
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Christoph Lameter authored
This is a new slab allocator which was motivated by the complexity of the existing code in mm/slab.c. It attempts to address a variety of concerns with the existing implementation. A. Management of object queues A particular concern was the complex management of the numerous object queues in SLAB. SLUB has no such queues. Instead we dedicate a slab for each allocating CPU and use objects from a slab directly instead of queueing them up. B. Storage overhead of object queues SLAB Object queues exist per node, per CPU. The alien cache queue even has a queue array that contain a queue for each processor on each node. For very large systems the number of queues and the number of objects that may be caught in those queues grows exponentially. On our systems with 1k nodes / processors we have several gigabytes just tied up for storing references to objects for those queues This does not include the objects that could be on those queues. One fears that the whole memory of the machine could one day be consumed by those queues. C. SLAB meta data overhead SLAB has overhead at the beginning of each slab. This means that data cannot be naturally aligned at the beginning of a slab block. SLUB keeps all meta data in the corresponding page_struct. Objects can be naturally aligned in the slab. F.e. a 128 byte object will be aligned at 128 byte boundaries and can fit tightly into a 4k page with no bytes left over. SLAB cannot do this. D. SLAB has a complex cache reaper SLUB does not need a cache reaper for UP systems. On SMP systems the per CPU slab may be pushed back into partial list but that operation is simple and does not require an iteration over a list of objects. SLAB expires per CPU, shared and alien object queues during cache reaping which may cause strange hold offs. E. SLAB has complex NUMA policy layer support SLUB pushes NUMA policy handling into the page allocator. This means that allocation is coarser (SLUB does interleave on a page level) but that situation was also present before 2.6.13. SLABs application of policies to individual slab objects allocated in SLAB is certainly a performance concern due to the frequent references to memory policies which may lead a sequence of objects to come from one node after another. SLUB will get a slab full of objects from one node and then will switch to the next. F. Reduction of the size of partial slab lists SLAB has per node partial lists. This means that over time a large number of partial slabs may accumulate on those lists. These can only be reused if allocator occur on specific nodes. SLUB has a global pool of partial slabs and will consume slabs from that pool to decrease fragmentation. G. Tunables SLAB has sophisticated tuning abilities for each slab cache. One can manipulate the queue sizes in detail. However, filling the queues still requires the uses of the spin lock to check out slabs. SLUB has a global parameter (min_slab_order) for tuning. Increasing the minimum slab order can decrease the locking overhead. The bigger the slab order the less motions of pages between per CPU and partial lists occur and the better SLUB will be scaling. G. Slab merging We often have slab caches with similar parameters. SLUB detects those on boot up and merges them into the corresponding general caches. This leads to more effective memory use. About 50% of all caches can be eliminated through slab merging. This will also decrease slab fragmentation because partial allocated slabs can be filled up again. Slab merging can be switched off by specifying slub_nomerge on boot up. Note that merging can expose heretofore unknown bugs in the kernel because corrupted objects may now be placed differently and corrupt differing neighboring objects. Enable sanity checks to find those. H. Diagnostics The current slab diagnostics are difficult to use and require a recompilation of the kernel. SLUB contains debugging code that is always available (but is kept out of the hot code paths). SLUB diagnostics can be enabled via the "slab_debug" option. Parameters can be specified to select a single or a group of slab caches for diagnostics. This means that the system is running with the usual performance and it is much more likely that race conditions can be reproduced. I. Resiliency If basic sanity checks are on then SLUB is capable of detecting common error conditions and recover as best as possible to allow the system to continue. J. Tracing Tracing can be enabled via the slab_debug=T,<slabcache> option during boot. SLUB will then protocol all actions on that slabcache and dump the object contents on free. K. On demand DMA cache creation. Generally DMA caches are not needed. If a kmalloc is used with __GFP_DMA then just create this single slabcache that is needed. For systems that have no ZONE_DMA requirement the support is completely eliminated. L. Performance increase Some benchmarks have shown speed improvements on kernbench in the range of 5-10%. The locking overhead of slub is based on the underlying base allocation size. If we can reliably allocate larger order pages then it is possible to increase slub performance much further. The anti-fragmentation patches may enable further performance increases. Tested on: i386 UP + SMP, x86_64 UP + SMP + NUMA emulation, IA64 NUMA + Simulator SLUB Boot options slub_nomerge Disable merging of slabs slub_min_order=x Require a minimum order for slab caches. This increases the managed chunk size and therefore reduces meta data and locking overhead. slub_min_objects=x Mininum objects per slab. Default is 8. slub_max_order=x Avoid generating slabs larger than order specified. slub_debug Enable all diagnostics for all caches slub_debug=<options> Enable selective options for all caches slub_debug=<o>,<cache> Enable selective options for a certain set of caches Available Debug options F Double Free checking, sanity and resiliency R Red zoning P Object / padding poisoning U Track last free / alloc T Trace all allocs / frees (only use for individual slabs). To use SLUB: Apply this patch and then select SLUB as the default slab allocator. [hugh@veritas.com: fix an oops-causing locking error] [akpm@linux-foundation.org: various stupid cleanups and small fixes] Signed-off-by:
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