- 13 Nov, 2013 40 commits
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Geert Uytterhoeven authored
It's already available in <linux/interrupt.h> Signed-off-by:
Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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Vineet Gupta authored
fpu_counter in task_struct was used only by sh/x86. Both of these now carry it in ARCH specific thread_struct, hence this can now be removed from generic task_struct, shrinking it slightly for other arches. Signed-off-by:
Vineet Gupta <vgupta@synopsys.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Paul Mundt <paul.mundt@gmail.com> Signed-off-by:
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Vineet Gupta authored
Only a couple of arches (sh/x86) use fpu_counter in task_struct so it can be moved out into ARCH specific thread_struct, reducing the size of task_struct for other arches. Compile tested i386_defconfig + gcc 4.7.3 Signed-off-by:
Ingo Molnar <mingo@kernel.org> Cc: Paul Mundt <paul.mundt@gmail.com> Signed-off-by:
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Vineet Gupta authored
Only a couple of arches (sh/x86) use fpu_counter in task_struct so it can be moved out into ARCH specific thread_struct, reducing the size of task_struct for other arches. Compile tested sh defconfig + sh4-linux-gcc (4.6.3) Signed-off-by:
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Roel Kluin authored
if (unlikely(x) > 0) doesn't seem to help branch prediction Signed-off-by:
Roel Kluin <roel.kluin@gmail.com> Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: "H. Peter Anvin" <hpa@linux.intel.com> Cc: Ingo Molnar <mingo@kernel.org> Signed-off-by:
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Geert Uytterhoeven authored
Commit 15d94b82 ("reboot: move shutdown/reboot related functions to kernel/reboot.c") moved all kexec-related functionality to kernel/reboot.c, so kernel/sys.c no longer needs to include <linux/kexec.h>. Signed-off-by:
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Chen Gang authored
The wrapper function delayacct_add_tsk() already checked 'tsk->delays', and __delayacct_add_tsk() has no another direct callers, so can remove the redundancy checking code. And the label 'done' is also useless, so remove it, too. Signed-off-by:
Chen Gang <gang.chen@asianux.com> Signed-off-by:
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Michal Nazarewicz authored
getenv() may return NULL if given environment variable does not exist which leads to NULL dereference when calling strncat. Besides that, the environment variable name was copied to a temporary env_var buffer, but this copying can be avoided by simply using the input string. Lastly, the whole loop can be greatly simplified by using the snprintf function instead of the playing with strncat. By the way, the current implementation allows a recursive variable expansion, as in: $ echo 'out ${A} out ' | A='a ${B} a' B=b /tmp/a out a b a out I'm assuming this is just a side effect and not a conscious decision (especially as this may lead to infinite loop), but I didn't want to change this behaviour without consulting. If the current behaviour is deamed incorrect, I'll be happy to send a patch without recursive processing. Signed-off-by:Michal Nazarewicz <mina86@mina86.com> Cc: Kees Cook <keescook@chromium.org> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Jesper Juhl <jj@codesealer.com> Signed-off-by:
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Eric Sandeen authored
glibc recently changed the error string for ESTALE to remove "NFS" - https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=96945714ec61951cc748da2b4b8a80cf02127ee9 from: [ERR_REMAP (ESTALE)] = N_("Stale NFS file handle"), to: [ERR_REMAP (ESTALE)] = N_("Stale file handle"), And some have expressed concern that the kernel's errno.h comments still refer to NFS. So make that change... note that this is a comment-only change, and has no functional difference. Signed-off-by:
Eric Sandeen <sandeen@redhat.com> Signed-off-by:
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Sebastian Capella authored
The name_to_dev_t function has a comment block which lists the supported syntaxes for the device name. Add a bullet for the <major>:<minor> syntax, which is already supported in the code Signed-off-by:
Sebastian Capella <sebastian.capella@linaro.org> Signed-off-by:
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Andi Kleen authored
For some reason I managed to trick gcc into create CRC symbols that are not absolute anymore, but weak. Make modpost handle this case. Signed-off-by:
Andi Kleen <ak@linux.intel.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> Signed-off-by:
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Andi Kleen authored
Use standard gcc __attribute__((alias(foo))) to define the syscall aliases instead of custom assembler macros. This is far cleaner, and also fixes my LTO kernel build. Signed-off-by:
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Michael Opdenacker authored
Who needs cramfs when you have squashfs? At least, we should warn people that cramfs is obsolete. Signed-off-by:
Michael Opdenacker <michael.opdenacker@free-electrons.com> Signed-off-by:
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Greg Thelen authored
Tests various percpu operations. Enable with CONFIG_PERCPU_TEST=m. Signed-off-by:
Greg Thelen <gthelen@google.com> Acked-by:
Tejun Heo <tj@kernel.org> Acked-by:
Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:
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Prarit Bhargava authored
The CONFIG_HPET_MMAP Kconfig option exposes the memory map of the HPET registers to userspace. The Kconfig help points out that in some cases this can be a security risk as some systems may erroneously configure the map such that additional data is exposed to userspace. This is a problem for distributions -- some users want the MMAP functionality but it comes with a significant security risk. In an effort to mitigate this risk, and due to the low number of users of the MMAP functionality, I've introduced a kernel parameter, hpet_mmap_enable, that is required in order to actually have the HPET MMAP exposed. Signed-off-by:
Prarit Bhargava <prarit@redhat.com> Acked-by:
Matt Wilson <msw@amazon.com> Signed-off-by:
Clemens Ladisch <clemens@ladisch.de> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Tomas Winkler <tomas.winkler@intel.com> Signed-off-by:
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Mel Gorman authored
Commit 0255d491 ("mm: Account for a THP NUMA hinting update as one PTE update") was added to account for the number of PTE updates when marking pages prot_numa. task_numa_work was using the old return value to track how much address space had been updated. Altering the return value causes the scanner to do more work than it is configured or documented to in a single unit of work. This patch reverts that commit and accounts for the number of THP updates separately in vmstat. It is up to the administrator to interpret the pair of values correctly. This is a straight-forward operation and likely to only be of interest when actively debugging NUMA balancing problems. The impact of this patch is that the NUMA PTE scanner will scan slower when THP is enabled and workloads may converge slower as a result. On the flip size system CPU usage should be lower than recent tests reported. This is an illustrative example of a short single JVM specjbb test specjbb 3.12.0 3.12.0 vanilla acctupdates TPut 1 26143.00 ( 0.00%) 25747.00 ( -1.51%) TPut 7 185257.00 ( 0.00%) 183202.00 ( -1.11%) TPut 13 329760.00 ( 0.00%) 346577.00 ( 5.10%) TPut 19 442502.00 ( 0.00%) 460146.00 ( 3.99%) TPut 25 540634.00 ( 0.00%) 549053.00 ( 1.56%) TPut 31 512098.00 ( 0.00%) 519611.00 ( 1.47%) TPut 37 461276.00 ( 0.00%) 474973.00 ( 2.97%) TPut 43 403089.00 ( 0.00%) 414172.00 ( 2.75%) 3.12.0 3.12.0 vanillaacctupdates User 5169.64 5184.14 System 100.45 80.02 Elapsed 252.75 251.85 Performance is similar but note the reduction in system CPU time. While this showed a performance gain, it will not be universal but at least it'll be behaving as documented. The vmstats are obviously different but here is an obvious interpretation of them from mmtests. 3.12.0 3.12.0 vanillaacctupdates NUMA page range updates 1408326 11043064 NUMA huge PMD updates 0 21040 NUMA PTE updates 1408326 291624 "NUMA page range updates" == nr_pte_updates and is the value returned to the NUMA pte scanner. NUMA huge PMD updates were the number of THP updates which in combination can be used to calculate how many ptes were updated from userspace. Signed-off-by:
Mel Gorman <mgorman@suse.de> Reported-by:
Alex Thorlton <athorlton@sgi.com> Reviewed-by:
Rik van Riel <riel@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by:
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Jerome Marchand authored
The same calculation is currently done in three differents places. Factor that code so future changes has to be made at only one place. [akpm@linux-foundation.org: uninline vm_commit_limit()] Signed-off-by:
Jerome Marchand <jmarchan@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by:
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Zheng Liu authored
Now dirty_background_ratio/dirty_ratio contains a percentage of total avaiable memory, which contains free pages and reclaimable pages. The number of these pages is not equal to the number of total system memory. But they are described as a percentage of total system memory in Documentation/sysctl/vm.txt. So we need to fix them to avoid misunderstanding. Signed-off-by:
Zheng Liu <wenqing.lz@taobao.com> Cc: Rob Landley <rob@landley.net> Signed-off-by:
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Zhi Yong Wu authored
Signed-off-by:
Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> Signed-off-by:
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Zhi Yong Wu authored
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Weijie Yang authored
The refcount routine was not fit the kernel get/put semantic exactly, There were too many judgement statements on refcount and it could be minus. This patch does the following: - move refcount judgement to zswap_entry_put() to hide resource free function. - add a new function zswap_entry_find_get(), so that callers can use easily in the following pattern: zswap_entry_find_get .../* do something */ zswap_entry_put - to eliminate compile error, move some functions declaration This patch is based on Minchan Kim <minchan@kernel.org> 's idea and suggestion. Signed-off-by:Weijie Yang <weijie.yang@samsung.com> Cc: Seth Jennings <sjennings@variantweb.net> Acked-by:
Minchan Kim <minchan@kernel.org> Cc: Bob Liu <bob.liu@oracle.com> Signed-off-by:
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Weijie Yang authored
Consider the following scenario: thread 0: reclaim entry x (get refcount, but not call zswap_get_swap_cache_page) thread 1: call zswap_frontswap_invalidate_page to invalidate entry x. finished, entry x and its zbud is not freed as its refcount != 0 now, the swap_map[x] = 0 thread 0: now call zswap_get_swap_cache_page swapcache_prepare return -ENOENT because entry x is not used any more zswap_get_swap_cache_page return ZSWAP_SWAPCACHE_NOMEM zswap_writeback_entry do nothing except put refcount Now, the memory of zswap_entry x and its zpage leak. Modify: - check the refcount in fail path, free memory if it is not referenced. - use ZSWAP_SWAPCACHE_FAIL instead of ZSWAP_SWAPCACHE_NOMEM as the fail path can be not only caused by nomem but also by invalidate. Signed-off-by:
Bob Liu <bob.liu@oracle.com> Reviewed-by:
Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: <stable@vger.kernel.org> Signed-off-by:
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Qiang Huang authored
Signed-off-by:
Qiang Huang <h.huangqiang@huawei.com> Reviewed-by:
Pekka Enberg <penberg@kernel.org> Acked-by:
David Rientjes <rientjes@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Glauber Costa <glommer@parallels.com> Signed-off-by:
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Qiang Huang authored
We can't see the relationship with memcg from the parameters, so the name with memcg_idx would be more reasonable. Signed-off-by:
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Qiang Huang authored
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Akira Takeuchi authored
This patch fixes the problem that get_unmapped_area() can return illegal address and result in failing mmap(2) etc. In case that the address higher than PAGE_SIZE is set to /proc/sys/vm/mmap_min_addr, the address lower than mmap_min_addr can be returned by get_unmapped_area(), even if you do not pass any virtual address hint (i.e. the second argument). This is because the current get_unmapped_area() code does not take into account mmap_min_addr. This leads to two actual problems as follows: 1. mmap(2) can fail with EPERM on the process without CAP_SYS_RAWIO, although any illegal parameter is not passed. 2. The bottom-up search path after the top-down search might not work in arch_get_unmapped_area_topdown(). Note: The first and third chunk of my patch, which changes "len" check, are for more precise check using mmap_min_addr, and not for solving the above problem. [How to reproduce] --- test.c ------------------------------------------------- #include <stdio.h> #include <unistd.h> #include <sys/mman.h> #include <sys/errno.h> int main(int argc, char *argv[]) { void *ret = NULL, *last_map; size_t pagesize = sysconf(_SC_PAGESIZE); do { last_map = ret; ret = mmap(0, pagesize, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); // printf("ret=%p\n", ret); } while (ret != MAP_FAILED); if (errno != ENOMEM) { printf("ERR: unexpected errno: %d (last map=%p)\n", errno, last_map); } return 0; } --------------------------------------------------------------- $ gcc -m32 -o test test.c $ sudo sysctl -w vm.mmap_min_addr=65536 vm.mmap_min_addr = 65536 $ ./test (run as non-priviledge user) ERR: unexpected errno: 1 (last map=0x10000) Signed-off-by:Akira Takeuchi <takeuchi.akr@jp.panasonic.com> Signed-off-by:
Kiyoshi Owada <owada.kiyoshi@jp.panasonic.com> Reviewed-by:
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: <stable@vger.kernel.org> Signed-off-by:
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KOSAKI Motohiro authored
When __rmqueue_fallback() doesn't find a free block with the required size it splits a larger page and puts the rest of the page onto the free list. But it has one serious mistake. When putting back, __rmqueue_fallback() always use start_migratetype if type is not CMA. However, __rmqueue_fallback() is only called when all of the start_migratetype queue is empty. That said, __rmqueue_fallback always puts back memory to the wrong queue except try_to_steal_freepages() changed pageblock type (i.e. requested size is smaller than half of page block). The end result is that the antifragmentation framework increases fragmenation instead of decreasing it. Mel's original anti fragmentation does the right thing. But commit 47118af0 ("mm: mmzone: MIGRATE_CMA migration type added") broke it. This patch restores sane and old behavior. It also removes an incorrect comment which was introduced by commit fef903ef ("mm/page_alloc.c: restructure free-page stealing code and fix a bug"). Signed-off-by:
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Nazarewicz <mina86@mina86.com> Signed-off-by:
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KOSAKI Motohiro authored
In general, every tracepoint should be zero overhead if it is disabled. However, trace_mm_page_alloc_extfrag() is one of exception. It evaluate "new_type == start_migratetype" even if tracepoint is disabled. However, the code can be moved into tracepoint's TP_fast_assign() and TP_fast_assign exist exactly such purpose. This patch does it. Signed-off-by:
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KOSAKI Motohiro authored
Currently, set_pageblock_migratetype() screws up MIGRATE_CMA and MIGRATE_ISOLATE if page_group_by_mobility_disabled is true. It rewrites the argument to MIGRATE_UNMOVABLE and we lost these attribute. The problem was introduced by commit 49255c61 ("page allocator: move check for disabled anti-fragmentation out of fastpath"). So a 4 year old issue may mean that nobody uses page_group_by_mobility_disabled. But anyway, this patch fixes the problem. Signed-off-by:
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Damien Ramonda authored
The kernel's readahead algorithm sometimes interprets random read accesses as sequential and triggers unnecessary data prefecthing from storage device (impacting random read average latency). In order to identify sequential cache read misses, the readahead algorithm intends to check whether offset - previous offset == 1 (trivial sequential reads) or offset - previous offset == 0 (sequential reads not aligned on page boundary): if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL) The current offset is stored in the "offset" variable of type "pgoff_t" (unsigned long), while previous offset is stored in "ra->prev_pos" of type "loff_t" (long long). Therefore, operands of the if statement are implicitly converted to type long long. Consequently, when previous offset > current offset (which happens on random pattern), the if condition is true and access is wrongly interpeted as sequential. An unnecessary data prefetching is triggered, impacting the average random read latency. Storing the previous offset value in a "pgoff_t" variable (unsigned long) fixes the sequential read detection logic. Signed-off-by:
Damien Ramonda <damien.ramonda@intel.com> Reviewed-by:
Fengguang Wu <fengguang.wu@intel.com> Acked-by:
Pierre Tardy <pierre.tardy@intel.com> Acked-by:
David Cohen <david.a.cohen@linux.intel.com> Signed-off-by:
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Mel Gorman authored
It has been reported on very large machines that show_mem is taking almost 5 minutes to display information. This is a serious problem if there is an OOM storm. The bulk of the cost is in show_mem doing a very expensive PFN walk to give us the following information Total RAM: Also available as totalram_pages Highmem pages: Also available as totalhigh_pages Reserved pages: Can be inferred from the zone structure Shared pages: PFN walk required Unshared pages: PFN walk required Quick pages: Per-cpu walk required Only the shared/unshared pages requires a full PFN walk but that information is useless. It is also inaccurate as page pins of unshared pages would be accounted for as shared. Even if the information was accurate, I'm struggling to think how the shared/unshared information could be useful for debugging OOM conditions. Maybe it was useful before rmap existed when reclaiming shared pages was costly but it is less relevant today. The PFN walk could be optimised a bit but why bother as the information is useless. This patch deletes the PFN walker and infers the total RAM, highmem and reserved pages count from struct zone. It omits the shared/unshared page usage on the grounds that it is useless. It also corrects the reporting of HighMem as HighMem/MovableOnly as ZONE_MOVABLE has similar problems to HighMem with respect to lowmem/highmem exhaustion. Signed-off-by:
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Daeseok Youn authored
Signed-off-by:
Daeseok Youn <daeseok.youn@gmail.com> Signed-off-by:
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Toshi Kani authored
vmstat_cpuup_callback() is a CPU notifier callback, which marks N_CPU to a node at CPU online event. However, it does not update this N_CPU info at CPU offline event. Changed vmstat_cpuup_callback() to clear N_CPU when the last CPU in the node is put into offline, i.e. the node no longer has any online CPU. Signed-off-by:
Toshi Kani <toshi.kani@hp.com> Acked-by:
Christoph Lameter <cl@linux.com> Reviewed-by:
Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Tested-by:
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Toshi Kani authored
After a system booted, N_CPU is not set to any node as has_cpu shows an empty line. # cat /sys/devices/system/node/has_cpu (show-empty-line) setup_vmstat() registers its CPU notifier callback, vmstat_cpuup_callback(), which marks N_CPU to a node when a CPU is put into online. However, setup_vmstat() is called after all CPUs are launched in the boot sequence. Changed setup_vmstat() to mark N_CPU to the nodes with online CPUs at boot, which is consistent with other operations in vmstat_cpuup_callback(), i.e. start_cpu_timer() and refresh_zone_stat_thresholds(). Also added get_online_cpus() to protect the for_each_online_cpu() loop. Signed-off-by:
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Tang Chen authored
The hot-Pluggable field in SRAT specifies which memory is hotpluggable. As we mentioned before, if hotpluggable memory is used by the kernel, it cannot be hot-removed. So memory hotplug users may want to set all hotpluggable memory in ZONE_MOVABLE so that the kernel won't use it. Memory hotplug users may also set a node as movable node, which has ZONE_MOVABLE only, so that the whole node can be hot-removed. But the kernel cannot use memory in ZONE_MOVABLE. By doing this, the kernel cannot use memory in movable nodes. This will cause NUMA performance down. And other users may be unhappy. So we need a way to allow users to enable and disable this functionality. In this patch, we introduce movable_node boot option to allow users to choose to not to consume hotpluggable memory at early boot time and later we can set it as ZONE_MOVABLE. To achieve this, the movable_node boot option will control the memblock allocation direction. That said, after memblock is ready, before SRAT is parsed, we should allocate memory near the kernel image as we explained in the previous patches. So if movable_node boot option is set, the kernel does the following: 1. After memblock is ready, make memblock allocate memory bottom up. 2. After SRAT is parsed, make memblock behave as default, allocate memory top down. Users can specify "movable_node" in kernel commandline to enable this functionality. For those who don't use memory hotplug or who don't want to lose their NUMA performance, just don't specify anything. The kernel will work as before. Signed-off-by:
Tang Chen <tangchen@cn.fujitsu.com> Signed-off-by:
Zhang Yanfei <zhangyanfei@cn.fujitsu.com> Suggested-by:
Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Suggested-by:
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Tang Chen authored
Memory reserved for crashkernel could be large. So we should not allocate this memory bottom up from the end of kernel image. When SRAT is parsed, we will be able to know which memory is hotpluggable, and we can avoid allocating this memory for the kernel. So reorder reserve_crashkernel() after SRAT is parsed. Signed-off-by:
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Tang Chen authored
The Linux kernel cannot migrate pages used by the kernel. As a result, kernel pages cannot be hot-removed. So we cannot allocate hotpluggable memory for the kernel. In a memory hotplug system, any numa node the kernel resides in should be unhotpluggable. And for a modern server, each node could have at least 16GB memory. So memory around the kernel image is highly likely unhotpluggable. ACPI SRAT (System Resource Affinity Table) contains the memory hotplug info. But before SRAT is parsed, memblock has already started to allocate memory for the kernel. So we need to prevent memblock from doing this. So direct memory mapping page tables setup is the case. init_mem_mapping() is called before SRAT is parsed. To prevent page tables being allocated within hotpluggable memory, we will use bottom-up direction to allocate page tables from the end of kernel image to the higher memory. Note: As for allocating page tables in lower memory, TJ said: : This is an optional behavior which is triggered by a very specific kernel : boot param, which I suspect is gonna need to stick around to support : memory hotplug in the current setup unless we add another layer of address : translation to support memory hotplug. As for page tables may occupy too much lower memory if using 4K mapping (CONFIG_DEBUG_PAGEALLOC and CONFIG_KMEMCHECK both disable using >4k pages), TJ said: : But as I said in the same paragraph, parsing SRAT earlier doesn't solve : the problem in itself either. Ignoring the option if 4k mapping is : required and memory consumption would be prohibitive should work, no? : Something like that would be necessary if we're gonna worry about cases : like this no matter how we implement it, but, frankly, I'm not sure this : is something worth worrying about. Signed-off-by:
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Tang Chen authored
Create a new function memory_map_top_down to factor out of the top-down direct memory mapping pagetable setup. This is also a preparation for the following patch, which will introduce the bottom-up memory mapping. That said, we will put the two ways of pagetable setup into separate functions, and choose to use which way in init_mem_mapping, which makes the code more clear. Signed-off-by:
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Tang Chen authored
The Linux kernel cannot migrate pages used by the kernel. As a result, kernel pages cannot be hot-removed. So we cannot allocate hotpluggable memory for the kernel. ACPI SRAT (System Resource Affinity Table) contains the memory hotplug info. But before SRAT is parsed, memblock has already started to allocate memory for the kernel. So we need to prevent memblock from doing this. In a memory hotplug system, any numa node the kernel resides in should be unhotpluggable. And for a modern server, each node could have at least 16GB memory. So memory around the kernel image is highly likely unhotpluggable. So the basic idea is: Allocate memory from the end of the kernel image and to the higher memory. Since memory allocation before SRAT is parsed won't be too much, it could highly likely be in the same node with kernel image. The current memblock can only allocate memory top-down. So this patch introduces a new bottom-up allocation mode to allocate memory bottom-up. And later when we use this allocation direction to allocate memory, we will limit the start address above the kernel. Signed-off-by:
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Tang Chen authored
[Problem] The current Linux cannot migrate pages used by the kernel because of the kernel direct mapping. In Linux kernel space, va = pa + PAGE_OFFSET. When the pa is changed, we cannot simply update the pagetable and keep the va unmodified. So the kernel pages are not migratable. There are also some other issues will cause the kernel pages not migratable. For example, the physical address may be cached somewhere and will be used. It is not to update all the caches. When doing memory hotplug in Linux, we first migrate all the pages in one memory device somewhere else, and then remove the device. But if pages are used by the kernel, they are not migratable. As a result, memory used by the kernel cannot be hot-removed. Modifying the kernel direct mapping mechanism is too difficult to do. And it may cause the kernel performance down and unstable. So we use the following way to do memory hotplug. [What we are doing] In Linux, memory in one numa node is divided into several zones. One of the zones is ZONE_MOVABLE, which the kernel won't use. In order to implement memory hotplug in Linux, we are going to arrange all hotpluggable memory in ZONE_MOVABLE so that the kernel won't use these memory. To do this, we need ACPI's help. In ACPI, SRAT(System Resource Affinity Table) contains NUMA info. The memory affinities in SRAT record every memory range in the system, and also, flags specifying if the memory range is hotpluggable. (Please refer to ACPI spec 5.0 5.2.16) With the help of SRAT, we have to do the following two things to achieve our goal: 1. When doing memory hot-add, allow the users arranging hotpluggable as ZONE_MOVABLE. (This has been done by the MOVABLE_NODE functionality in Linux.) 2. when the system is booting, prevent bootmem allocator from allocating hotpluggable memory for the kernel before the memory initialization finishes. The problem 2 is the key problem we are going to solve. But before solving it, we need some preparation. Please see below. [Preparation] Bootloader has to load the kernel image into memory. And this memory must be unhotpluggable. We cannot prevent this anyway. So in a memory hotplug system, we can assume any node the kernel resides in is not hotpluggable. Before SRAT is parsed, we don't know which memory ranges are hotpluggable. But memblock has already started to work. In the current kernel, memblock allocates the following memory before SRAT is parsed: setup_arch() |->memblock_x86_fill() /* memblock is ready */ |...... |->early_reserve_e820_mpc_new() /* allocate memory under 1MB */ |->reserve_real_mode() /* allocate memory under 1MB */ |->init_mem_mapping() /* allocate page tables, about 2MB to map 1GB memory */ |->dma_contiguous_reserve() /* specified by user, should be low */ |->setup_log_buf() /* specified by user, several mega bytes */ |->relocate_initrd() /* could be large, but will be freed after boot, should reorder */ |->acpi_initrd_override() /* several mega bytes */ |->reserve_crashkernel() /* could be large, should reorder */ |...... |->initmem_init() /* Parse SRAT */ According to Tejun's advice, before SRAT is parsed, we should try our best to allocate memory near the kernel image. Since the whole node the kernel resides in won't be hotpluggable, and for a modern server, a node may have at least 16GB memory, allocating several mega bytes memory around the kernel image won't cross to hotpluggable memory. [About this patchset] So this patchset is the preparation for the problem 2 that we want to solve. It does the following: 1. Make memblock be able to allocate memory bottom up. 1) Keep all the memblock APIs' prototype unmodified. 2) When the direction is bottom up, keep the start address greater than the end of kernel image. 2. Improve init_mem_mapping() to support allocate page tables in bottom up direction. 3. Introduce "movable_node" boot option to enable and disable this functionality. This patch (of 6): Create a new function __memblock_find_range_top_down to factor out of top-down allocation from memblock_find_in_range_node. This is a preparation because we will introduce a new bottom-up allocation mode in the following patch. Signed-off-by:
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