The quilt patch titled
Subject: mm: reclaim mustn't enter FS for SWP_FS_OPS swap-space
has been removed from the -mm tree. Its filename was
mm-reclaim-mustnt-enter-fs-for-swp_fs_ops-swap-space.patch
This patch was dropped because it was merged into mm-stable
------------------------------------------------------
From: NeilBrown <neilb@xxxxxxx>
Subject: 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variable becoming out-of-date.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@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: David Howells <dhowells@xxxxxxxxxx>
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap.h | 8 ++++++++
mm/vmscan.c | 29 ++++++++++++++++++++---------
2 files changed, 28 insertions(+), 9 deletions(-)
--- a/mm/swap.h~mm-reclaim-mustnt-enter-fs-for-swp_fs_ops-swap-space
+++ a/mm/swap.h
@@ -50,6 +50,10 @@ struct page *swap_cluster_readahead(swp_
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_swa
{
}
+static inline unsigned int page_swap_flags(struct page *page)
+{
+ return 0;
+}
#endif /* CONFIG_SWAP */
#endif /* _MM_SWAP_H */
--- a/mm/vmscan.c~mm-reclaim-mustnt-enter-fs-for-swp_fs_ops-swap-space
+++ a/mm/vmscan.c
@@ -1502,6 +1502,22 @@ static unsigned int demote_page_list(str
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;
_
Patches currently in -mm which might be from neilb@xxxxxxx are
mm-discard-__gfp_atomic.patch
