Commit 8745d7f6 authored by Joao Martins's avatar Joao Martins Committed by Linus Torvalds

mm/gup: add compound page list iterator

Patch series "mm/gup: page unpining improvements", v4.

This series improves page unpinning, with an eye on improving MR
deregistration for big swaths of memory (which is bound by the page
unpining), particularly:

1) Decrement the head page by @ntails and thus reducing a lot the
   number of atomic operations per compound page.  This is done by
   comparing individual tail pages heads, and counting number of
   consecutive tails on which they match heads and based on that update
   head page refcount.  Should have a visible improvement in all page
   (un)pinners which use compound pages

2) Introducing a new API for unpinning page ranges (to avoid the trick
   in the previous item and be based on math), and use that in RDMA
   ib_mem_release (used for mr deregistration).

Performance improvements: unpin_user_pages() for hugetlbfs and THP
improves ~3x (through gup_test) and RDMA MR dereg improves ~4.5x with the
new API.  See patches 2 and 4 for those.

This patch (of 4):

Add a helper that iterates over head pages in a list of pages.  It
essentially counts the tails until the next page to process has a
different head that the current.  This is going to be used by
unpin_user_pages() family of functions, to batch the head page refcount
updates once for all passed consecutive tail pages.

Link: https://lkml.kernel.org/r/20210212130843.13865-1-joao.m.martins@oracle.com
Link: https://lkml.kernel.org/r/20210212130843.13865-2-joao.m.martins@oracle.comSigned-off-by: default avatarJoao Martins <joao.m.martins@oracle.com>
Suggested-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Reviewed-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f6899bc0
......@@ -213,6 +213,32 @@ void unpin_user_page(struct page *page)
}
EXPORT_SYMBOL(unpin_user_page);
static inline void compound_next(unsigned long i, unsigned long npages,
struct page **list, struct page **head,
unsigned int *ntails)
{
struct page *page;
unsigned int nr;
if (i >= npages)
return;
page = compound_head(list[i]);
for (nr = i + 1; nr < npages; nr++) {
if (compound_head(list[nr]) != page)
break;
}
*head = page;
*ntails = nr - i;
}
#define for_each_compound_head(__i, __list, __npages, __head, __ntails) \
for (__i = 0, \
compound_next(__i, __npages, __list, &(__head), &(__ntails)); \
__i < __npages; __i += __ntails, \
compound_next(__i, __npages, __list, &(__head), &(__ntails)))
/**
* unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
* @pages: array of pages to be maybe marked dirty, and definitely released.
......
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