From: Shakeel Butt <shakeelb@google.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@suse.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] mm: memcontrol: skip moving non-present pages that are mapped elsewhere
Date: Wed, 7 Dec 2022 16:36:07 -0800 [thread overview]
Message-ID: <CALvZod4RxpYOeVurV-vrTc7MY7m8tDCJPOsX+JNGv5BsuFMEFA@mail.gmail.com> (raw)
In-Reply-To: <20221206171340.139790-2-hannes@cmpxchg.org>
On Tue, Dec 6, 2022 at 9:14 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> During charge moving, the pte lock and the page lock cover nearly all
> cases of stabilizing page_mapped(). The only exception is when we're
> looking at a non-present pte and find a page in the page cache or in
> the swapcache: if the page is mapped elsewhere, it can become unmapped
> outside of our control. For this reason, rmap needs lock_page_memcg().
>
> We don't like cgroup-specific locks in generic MM code - especially in
> performance-critical MM code - and for a legacy feature that's
> unlikely to have many users left - if any.
>
> So remove the exception. Arguably that's better semantics anyway: the
> page is shared, and another process seems to be the more active user.
>
> Once we stop moving such pages, rmap doesn't need lock_page_memcg()
> anymore. The next patch will remove it.
>
> Suggested-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeelb@google.com>
next prev parent reply other threads:[~2022-12-08 0:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-06 17:13 [PATCH v2 0/3] mm: push down lock_page_memcg() Johannes Weiner
2022-12-06 17:13 ` [PATCH 1/3] mm: memcontrol: skip moving non-present pages that are mapped elsewhere Johannes Weiner
2022-12-07 1:51 ` Hugh Dickins
2022-12-08 0:36 ` Shakeel Butt [this message]
2022-12-06 17:13 ` [PATCH 2/3] mm: rmap: remove lock_page_memcg() Johannes Weiner
2022-12-07 1:52 ` Hugh Dickins
2022-12-08 0:36 ` Shakeel Butt
2022-12-06 17:13 ` [PATCH 3/3] mm: memcontrol: deprecate charge moving Johannes Weiner
2022-12-07 0:03 ` Shakeel Butt
2022-12-07 21:51 ` Andrew Morton
2022-12-07 22:15 ` Shakeel Butt
2022-12-07 1:58 ` Hugh Dickins
2022-12-07 13:00 ` Johannes Weiner
2022-12-07 14:07 ` [PATCH v2 0/3] mm: push down lock_page_memcg() Michal Hocko
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