Commit 01626a18 authored by Barry Song's avatar Barry Song Committed by Andrew Morton
Browse files

mm: avoid unconditional one-tick sleep when swapcache_prepare fails 

Commit 13ddaf26 ("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.

[v-songbaohua@oppo.com: wake_up only when swapcache_wq waitqueue is active]
  Link: https://lkml.kernel.org/r/20241008130807.40833-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240926211936.75373-1-21cnbao@gmail.com


Fixes: 13ddaf26 ("mm/swap: fix race when skipping swapcache")
Signed-off-by: default avatarBarry Song <v-songbaohua@oppo.com>
Reported-by: default avatarOven Liyang <liyangouwen1@oppo.com>
Tested-by: default avatarOven Liyang <liyangouwen1@oppo.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 18343007

mm/memory.c

+13 −2
Original line number Diff line number Diff line
@@ -4187,6 +4187,8 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf) 
}

#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.
@@ -4199,6 +4201,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 
{

	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;
@@ -4297,7 +4300,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 
					 * 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;
@@ -4604,8 +4609,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 
		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);

		if (waitqueue_active(&swapcache_wq))

			wake_up(&swapcache_wq);

	}

	if (si)

		put_swap_device(si);

	return ret;
@@ -4620,8 +4628,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 
		folio_unlock(swapcache);

		folio_put(swapcache);

	}

	if (need_clear_cache)

	if (need_clear_cache) {

		swapcache_clear(si, entry, nr_pages);

		if (waitqueue_active(&swapcache_wq))

			wake_up(&swapcache_wq);

	}

	if (si)

		put_swap_device(si);

	return ret;