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shmem: add huge pages support

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Here's basic implementation of huge pages support for shmem/tmpfs.

It's all pretty streight-forward:

  - shmem_getpage() allcoates huge page if it can and try to inserd into
    radix tree with shmem_add_to_page_cache();

  - shmem_add_to_page_cache() puts the page onto radix-tree if there's
    space for it;

  - shmem_undo_range() removes huge pages, if it fully within range.
    Partial truncate of huge pages zero out this part of THP.

    This have visible effect on fallocate(FALLOC_FL_PUNCH_HOLE)
    behaviour. As we don't really create hole in this case,
    lseek(SEEK_HOLE) may have inconsistent results depending what
    pages happened to be allocated.

  - no need to change shmem_fault: core-mm will map an compound page as
    huge if VMA is suitable;

Link: http://lkml.kernel.org/r/1466021202-61880-30-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Kirill A. Shutemov 2016-07-26 15:26:18 -07:00 • committed by Linus Torvalds
commit 800d8c63b2
9 changed files with 331 additions and 70 deletions
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7
mm/filemap.c
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@ -219,8 +219,13 @@ void __delete_from_page_cache(struct page *page, void *shadow)
/* hugetlb pages do not participate in page cache accounting. */
if (!PageHuge(page))
__mod_zone_page_state(page_zone(page), NR_FILE_PAGES, -nr);
if (PageSwapBacked(page))
if (PageSwapBacked(page)) {
__mod_zone_page_state(page_zone(page), NR_SHMEM, -nr);
if (PageTransHuge(page))
__dec_zone_page_state(page, NR_SHMEM_THPS);
} else {
VM_BUG_ON_PAGE(PageTransHuge(page) && !PageHuge(page), page);
}
/*
* At this point page must be either written or cleaned by truncate.