The patch titled
Subject: mm: avoid unconditional one-tick sleep when swapcache_prepare fails
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-avoid-unconditional-one-tick-sleep-when-swapcache_prepare-fails.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-avoid-unconditional-one-tick-sleep-when-swapcache_prepare-fails.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Barry Song <v-songbaohua@xxxxxxxx>
Subject: mm: avoid unconditional one-tick sleep when swapcache_prepare fails
Date: Fri, 27 Sep 2024 09:19:36 +1200
Commit 13ddaf26be32 ("mm/swap: fix race when skipping swapcache")
introduced an unconditional one-tick sleep when `swapcache_prepare()`
fails, which has led to reports of UI stuttering on latency-sensitive
Android devices. To address this, we can use a waitqueue to wake up tasks
that fail `swapcache_prepare()` sooner, instead of always sleeping for a
full tick. While tasks may occasionally be woken by an unrelated
`do_swap_page()`, this method is preferable to two scenarios: rapid
re-entry into page faults, which can cause livelocks, and multiple
millisecond sleeps, which visibly degrade user experience.
Oven's testing shows that a single waitqueue resolves the UI stuttering
issue. If a 'thundering herd' problem becomes apparent later, a waitqueue
hash similar to `folio_wait_table[PAGE_WAIT_TABLE_SIZE]` for page bit
locks can be introduced.
Link: https://lkml.kernel.org/r/20240926211936.75373-1-21cnbao@xxxxxxxxx
Fixes: 13ddaf26be32 ("mm/swap: fix race when skipping swapcache")
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Reported-by: Oven Liyang <liyangouwen1@xxxxxxxx>
Tested-by: Oven Liyang <liyangouwen1@xxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
--- a/mm/memory.c~mm-avoid-unconditional-one-tick-sleep-when-swapcache_prepare-fails
+++ a/mm/memory.c
@@ -4192,6 +4192,8 @@ static struct folio *alloc_swap_folio(st
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+static DECLARE_WAIT_QUEUE_HEAD(swapcache_wq);
+
/*
* We enter with non-exclusive mmap_lock (to exclude vma changes,
* but allow concurrent faults), and pte mapped but not yet locked.
@@ -4204,6 +4206,7 @@ vm_fault_t do_swap_page(struct vm_fault
{
struct vm_area_struct *vma = vmf->vma;
struct folio *swapcache, *folio = NULL;
+ DECLARE_WAITQUEUE(wait, current);
struct page *page;
struct swap_info_struct *si = NULL;
rmap_t rmap_flags = RMAP_NONE;
@@ -4302,7 +4305,9 @@ vm_fault_t do_swap_page(struct vm_fault
* Relax a bit to prevent rapid
* repeated page faults.
*/
+ add_wait_queue(&swapcache_wq, &wait);
schedule_timeout_uninterruptible(1);
+ remove_wait_queue(&swapcache_wq, &wait);
goto out_page;
}
need_clear_cache = true;
@@ -4609,8 +4614,10 @@ unlock:
pte_unmap_unlock(vmf->pte, vmf->ptl);
out:
/* Clear the swap cache pin for direct swapin after PTL unlock */
- if (need_clear_cache)
+ if (need_clear_cache) {
swapcache_clear(si, entry, nr_pages);
+ wake_up(&swapcache_wq);
+ }
if (si)
put_swap_device(si);
return ret;
@@ -4625,8 +4632,10 @@ out_release:
folio_unlock(swapcache);
folio_put(swapcache);
}
- if (need_clear_cache)
+ if (need_clear_cache) {
swapcache_clear(si, entry, nr_pages);
+ wake_up(&swapcache_wq);
+ }
if (si)
put_swap_device(si);
return ret;
_
Patches currently in -mm which might be from v-songbaohua@xxxxxxxx are
mm-avoid-unconditional-one-tick-sleep-when-swapcache_prepare-fails.patch
