Commit d144bf62 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: 779750d2 ("shmem: split huge pages beyond i_size under memory pressure")
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Reviewed-by: default avatarYang Shi <shy828301@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 050dcb5c

include/linux/shmem_fs.h

+13 −0
Original line number Diff line number Diff line
@@ -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);

mm/huge_memory.c

+4 −2
Original line number Diff line number Diff line
@@ -2454,11 +2454,11 @@ static void __split_huge_page(struct page *page, struct list_head *list, 


	for (i = nr - 1; i >= 1; i--) {

		__split_huge_page_tail(head, i, lruvec, list);

		/* Some pages can be beyond i_size: drop them from page cache */

		/* Some pages can be beyond EOF: drop them from page cache */

		if (head[i].index >= end) {

			ClearPageDirty(head + i);

			__delete_from_page_cache(head + i, NULL);

			if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))

			if (shmem_mapping(head->mapping))

				shmem_uncharge(head->mapping->host, 1);

			put_page(head + i);

		} else if (!PageAnon(page)) {
@@ -2686,6 +2686,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) 
		 * head page lock is good enough to serialize the trimming.

		 */

		end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);

		if (shmem_mapping(mapping))

			end = shmem_fallocend(mapping->host, end);

	}



	/*

mm/shmem.c

+14 −1
Original line number Diff line number Diff line
@@ -902,6 +902,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, 
	if (lend == -1)

		end = -1;	/* unsigned, so actually very big */



	if (info->fallocend > start && info->fallocend <= end && !unfalloc)

		info->fallocend = start;



	pagevec_init(&pvec);

	index = start;

	while (index < end && find_lock_entries(mapping, index, end - 1,
@@ -2650,7 +2653,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, 
	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

	struct shmem_inode_info *info = SHMEM_I(inode);

	struct shmem_falloc shmem_falloc;

	pgoff_t start, index, end;

	pgoff_t start, index, end, undo_fallocend;

	int error;



	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
@@ -2719,6 +2722,15 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, 
	inode->i_private = &shmem_falloc;

	spin_unlock(&inode->i_lock);



	/*

	 * info->fallocend is only relevant when huge pages might be

	 * involved: to prevent split_huge_page() freeing fallocated

	 * pages when FALLOC_FL_KEEP_SIZE committed beyond i_size.

	 */

	undo_fallocend = info->fallocend;

	if (info->fallocend < end)

		info->fallocend = end;



	for (index = start; index < end; ) {

		struct page *page;
@@ -2733,6 +2745,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, 
		else

			error = shmem_getpage(inode, index, &page, SGP_FALLOC);

		if (error) {

			info->fallocend = undo_fallocend;

			/* Remove the !PageUptodate pages we added */

			if (index > start) {

				shmem_undo_range(inode,