linux-kernel - Re: [PATCH] mm: avoid unconditional one-tick sleep when swapcache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <871q13qj2t.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Sun, 29 Sep 2024 10:39:38 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org,  Barry Song <v-songbaohua@...o.com>,
  Kairui Song <kasong@...cent.com>,  Yu Zhao <yuzhao@...gle.com>,  David
 Hildenbrand <david@...hat.com>,  Chris Li <chrisl@...nel.org>,  Hugh
 Dickins <hughd@...gle.com>,  Johannes Weiner <hannes@...xchg.org>,
  Matthew Wilcox <willy@...radead.org>,  Michal Hocko <mhocko@...e.com>,
  Minchan Kim <minchan@...nel.org>,  Yosry Ahmed <yosryahmed@...gle.com>,
  SeongJae Park <sj@...nel.org>,  Kalesh Singh <kaleshsingh@...gle.com>,
  Suren Baghdasaryan <surenb@...gle.com>,  stable@...r.kernel.org,  Oven
 Liyang <liyangouwen1@...o.com>
Subject: Re: [PATCH] mm: avoid unconditional one-tick sleep when
 swapcache_prepare fails

Hi, Barry,

Barry Song <21cnbao@...il.com> writes:

> From: Barry Song <v-songbaohua@...o.com>
>
> 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.

In general, I think that this works.  Why not extend the solution to
cover schedule_timeout_uninterruptible() in __read_swap_cache_async()
too?  We can call wake_up() when we clear SWAP_HAS_CACHE.  To avoid
overhead to call wake_up() when there's no task waiting, we can use an
atomic to count waiting tasks.

[snip]

--
Best Regards,
Huang, Ying