From d144bf6205342a4b5fed5d204ae18849a4de741b Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 2 Sep 2021 14:54:21 -0700 Subject: huge tmpfs: fix split_huge_page() after FALLOC_FL_KEEP_SIZE A successful shmem_fallocate() guarantees that the extent has been reserved, even beyond i_size when the FALLOC_FL_KEEP_SIZE flag was used. But that guarantee is broken by shmem_unused_huge_shrink()'s attempts to split huge pages and free their excess beyond i_size; and by other uses of split_huge_page() near i_size. It's sad to add a shmem inode field just for this, but I did not find a better way to keep the guarantee. A flag to say KEEP_SIZE has been used would be cheaper, but I'm averse to unclearable flags. The fallocend field is not perfect either (many disjoint ranges might be fallocated), but good enough; and gains another use later on. Link: https://lkml.kernel.org/r/ca9a146-3a59-6cd3-7f28-e9a044bb1052@google.com Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure") Signed-off-by: Hugh Dickins Reviewed-by: Yang Shi Cc: "Kirill A. Shutemov" Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Michal Hocko Cc: Mike Kravetz Cc: Rik van Riel Cc: Shakeel Butt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/shmem_fs.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'include') diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index 0a8499fb9c3c..bfc5899d18e0 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -18,6 +18,7 @@ struct shmem_inode_info { unsigned long flags; unsigned long alloced; /* data pages alloced to file */ unsigned long swapped; /* subtotal assigned to swap */ + pgoff_t fallocend; /* highest fallocate endindex */ struct list_head shrinklist; /* shrinkable hpage inodes */ struct list_head swaplist; /* chain of maybes on swap */ struct shared_policy policy; /* NUMA memory alloc policy */ @@ -119,6 +120,18 @@ static inline bool shmem_file(struct file *file) return shmem_mapping(file->f_mapping); } +/* + * If fallocate(FALLOC_FL_KEEP_SIZE) has been used, there may be pages + * beyond i_size's notion of EOF, which fallocate has committed to reserving: + * which split_huge_page() must therefore not delete. This use of a single + * "fallocend" per inode errs on the side of not deleting a reservation when + * in doubt: there are plenty of cases when it preserves unreserved pages. + */ +static inline pgoff_t shmem_fallocend(struct inode *inode, pgoff_t eof) +{ + return max(eof, SHMEM_I(inode)->fallocend); +} + extern bool shmem_charge(struct inode *inode, long pages); extern void shmem_uncharge(struct inode *inode, long pages); -- cgit v1.2.3