Commit d791ea67 authored by NeilBrown's avatar NeilBrown Committed by Andrew Morton
Browse files

mm: reclaim mustn't enter FS for SWP_FS_OPS swap-space 

If swap-out is using filesystem operations (SWP_FS_OPS), then it is not
safe to enter the FS for reclaim.  So only down-grade the requirement for
swap pages to __GFP_IO after checking that SWP_FS_OPS are not being used.

This makes the calculation of "may_enter_fs" slightly more complex, so
move it into a separate function.  with that done, there is little value
in maintaining the bool variable any more.  So replace the may_enter_fs
variable with a may_enter_fs() function.  This removes any risk for the
variable becoming out-of-date.

Link: https://lkml.kernel.org/r/164859778124.29473.16176717935781721855.stgit@noble.brown


Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Tested-by: default avatarDavid Howells <dhowells@redhat.com>
Tested-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4b60c0ff

mm/swap.h

+8 −0
Original line number Diff line number Diff line
@@ -50,6 +50,10 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t flag, 
struct page *swapin_readahead(swp_entry_t entry, gfp_t flag,

			      struct vm_fault *vmf);



static inline unsigned int page_swap_flags(struct page *page)

{

	return page_swap_info(page)->flags;

}

#else /* CONFIG_SWAP */

static inline int swap_readpage(struct page *page, bool do_poll)

{
@@ -129,5 +133,9 @@ static inline void clear_shadow_from_swap_cache(int type, unsigned long begin, 
{

}



static inline unsigned int page_swap_flags(struct page *page)

{

	return 0;

}

#endif /* CONFIG_SWAP */

#endif /* _MM_SWAP_H */

mm/vmscan.c

+20 −9
Original line number Diff line number Diff line
@@ -1502,6 +1502,22 @@ static unsigned int demote_page_list(struct list_head *demote_pages, 
	return nr_succeeded;

}



static bool may_enter_fs(struct page *page, gfp_t gfp_mask)

{

	if (gfp_mask & __GFP_FS)

		return true;

	if (!PageSwapCache(page) || !(gfp_mask & __GFP_IO))

		return false;

	/*

	 * We can "enter_fs" for swap-cache with only __GFP_IO

	 * providing this isn't SWP_FS_OPS.

	 * ->flags can be updated non-atomicially (scan_swap_map_slots),

	 * but that will never affect SWP_FS_OPS, so the data_race

	 * is safe.

	 */

	return !data_race(page_swap_flags(page) & SWP_FS_OPS);

}



/*

 * shrink_page_list() returns the number of reclaimed pages

 */
@@ -1528,7 +1544,7 @@ static unsigned int shrink_page_list(struct list_head *page_list, 
		struct page *page;

		struct folio *folio;

		enum page_references references = PAGEREF_RECLAIM;

		bool dirty, writeback, may_enter_fs;

		bool dirty, writeback;

		unsigned int nr_pages;



		cond_resched();
@@ -1553,9 +1569,6 @@ static unsigned int shrink_page_list(struct list_head *page_list, 
		if (!sc->may_unmap && page_mapped(page))

			goto keep_locked;



		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||

			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));



		/*

		 * The number of dirty pages determines if a node is marked

		 * reclaim_congested. kswapd will stall and start writing
@@ -1598,7 +1611,7 @@ static unsigned int shrink_page_list(struct list_head *page_list, 
		 *    not to fs). In this case mark the page for immediate

		 *    reclaim and continue scanning.

		 *

		 *    Require may_enter_fs because we would wait on fs, which

		 *    Require may_enter_fs() because we would wait on fs, which

		 *    may not have submitted IO yet. And the loop driver might

		 *    enter reclaim, and deadlock if it waits on a page for

		 *    which it is needed to do the write (loop masks off
@@ -1630,7 +1643,7 @@ static unsigned int shrink_page_list(struct list_head *page_list, 


			/* Case 2 above */

			} else if (writeback_throttling_sane(sc) ||

			    !PageReclaim(page) || !may_enter_fs) {

			    !PageReclaim(page) || !may_enter_fs(page, sc->gfp_mask)) {

				/*

				 * This is slightly racy - end_page_writeback()

				 * might have just cleared PageReclaim, then
@@ -1720,8 +1733,6 @@ static unsigned int shrink_page_list(struct list_head *page_list, 
						goto activate_locked_split;

				}



				may_enter_fs = true;



				/* Adding to swap updated mapping */

				mapping = page_mapping(page);

			}
@@ -1792,7 +1803,7 @@ static unsigned int shrink_page_list(struct list_head *page_list, 


			if (references == PAGEREF_RECLAIM_CLEAN)

				goto keep_locked;

			if (!may_enter_fs)

			if (!may_enter_fs(page, sc->gfp_mask))

				goto keep_locked;

			if (!sc->may_writepage)

				goto keep_locked;