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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variable becoming out-of-date.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: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
NeilBrown 2022-05-09 18:20:48 -07:00 committed by akpm
parent 4b60c0ff2f
commit d791ea676b
2 changed files with 28 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
mm/swap.h
View File

@ -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 */

29
mm/vmscan.c
View File

@ -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 @@ retry:
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 @@ retry:
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 @@ retry:
* 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 @@ retry:
/* 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 @@ retry:
goto activate_locked_split;
}
may_enter_fs = true;
/* Adding to swap updated mapping */
mapping = page_mapping(page);
}
@ -1792,7 +1803,7 @@ retry:
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;