From: Michal Hocko <mhocko@suse.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
akpm@linux-foundation.org, rientjes@google.com,
willy@infradead.org, guro@fb.com, riel@surriel.com,
minchan@kernel.org, kirill@shutemov.name, aarcange@redhat.com,
christian@brauner.io, hch@infradead.org, oleg@redhat.com,
david@redhat.com, jannh@google.com, shakeelb@google.com,
luto@kernel.org, christian.brauner@ubuntu.com,
fweimer@redhat.com, jengelh@inai.de, timmurray@google.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@android.com
Subject: Re: [PATCH 4/3] mm: drop MMF_OOM_SKIP from exit_mmap
Date: Thu, 30 Dec 2021 09:24:04 +0100 [thread overview]
Message-ID: <Yc1spBeXal373b4A@dhcp22.suse.cz> (raw)
In-Reply-To: <CAJuCfpEHJTqG+PkAPJknf5_41ZKFqjk8pY=gTg_VZgsfY-=9Tg@mail.gmail.com>
On Wed 29-12-21 21:59:55, Suren Baghdasaryan wrote:
[...]
> After some more digging I think there are two acceptable options:
>
> 1. Call unlock_range() under mmap_write_lock and then downgrade it to
> read lock so that both exit_mmap() and __oom_reap_task_mm() can unmap
> vmas in parallel like this:
>
> if (mm->locked_vm) {
> mmap_write_lock(mm);
> unlock_range(mm->mmap, ULONG_MAX);
> mmap_write_downgrade(mm);
> } else
> mmap_read_lock(mm);
> ...
> unmap_vmas(&tlb, vma, 0, -1);
> mmap_read_unlock(mm);
> mmap_write_lock(mm);
> free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
> ...
> mm->mmap = NULL;
> mmap_write_unlock(mm);
>
> This way exit_mmap() might block __oom_reap_task_mm() but for a much
> shorter time during unlock_range() call.
IIRC unlock_range depends on page lock at some stage and that can mean
this will block for a long time or for ever when the holder of the lock
depends on a memory allocation. This was the primary problem why the oom
reaper skips over mlocked vmas.
> 2. Introduce another vm_flag mask similar to VM_LOCKED which is set
> before munlock_vma_pages_range() clears VM_LOCKED so that
> __oom_reap_task_mm() can identify vmas being unlocked and skip them.
>
> Option 1 seems cleaner to me because it keeps the locking pattern
> around unlock_range() in exit_mmap() consistent with all other places
> it is used (in mremap() and munmap()) with mmap_write_lock taken.
> WDYT?
It would be really great to make unlock_range oom reaper aware IMHO.
You do not quote your change in the full length so it is not really
clear whether you are planning to drop __oom_reap_task_mm from exit_mmap
as well. If yes then 1) could push oom reaper to timeout while the
unlock_range could be dropped on something so that wouldn't be an
improvement. 2) sounds like a workaround to me as it doesn't really
address the underlying problem.
I have to say that I am not really a great fan of __oom_reap_task_mm in
exit_mmap but I would rather see it in place than making the surrounding
code more complex/tricky.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-12-30 8:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-08 21:22 [PATCH v4 1/3] mm: protect free_pgtables with mmap_lock write lock in exit_mmap Suren Baghdasaryan
2021-12-08 21:22 ` [PATCH v4 2/3] mm: document locking restrictions for vm_operations_struct::close Suren Baghdasaryan
2021-12-09 8:55 ` Michal Hocko
2021-12-08 21:22 ` [PATCH v4 3/3] mm/oom_kill: allow process_mrelease to run under mmap_lock protection Suren Baghdasaryan
2021-12-09 8:59 ` Michal Hocko
2021-12-09 19:03 ` Suren Baghdasaryan
2021-12-09 8:55 ` [PATCH v4 1/3] mm: protect free_pgtables with mmap_lock write lock in exit_mmap Michal Hocko
2021-12-09 19:03 ` Suren Baghdasaryan
2021-12-10 9:20 ` Michal Hocko
2021-12-09 9:12 ` [PATCH 4/3] mm: drop MMF_OOM_SKIP from exit_mmap Michal Hocko
2021-12-09 16:24 ` Suren Baghdasaryan
2021-12-09 16:47 ` Michal Hocko
2021-12-09 17:06 ` Suren Baghdasaryan
2021-12-16 2:26 ` Suren Baghdasaryan
2021-12-16 11:49 ` Johannes Weiner
2021-12-16 17:23 ` Suren Baghdasaryan
2021-12-30 5:59 ` Suren Baghdasaryan
2021-12-30 8:24 ` Michal Hocko [this message]
2021-12-30 17:29 ` Suren Baghdasaryan
2022-01-03 12:11 ` Michal Hocko
2022-01-03 21:16 ` Hugh Dickins
2022-01-04 22:24 ` Suren Baghdasaryan
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Yc1spBeXal373b4A@dhcp22.suse.cz \
--to=mhocko@suse.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=christian.brauner@ubuntu.com \
--cc=christian@brauner.io \
--cc=david@redhat.com \
--cc=fweimer@redhat.com \
--cc=guro@fb.com \
--cc=hannes@cmpxchg.org \
--cc=hch@infradead.org \
--cc=jannh@google.com \
--cc=jengelh@inai.de \
--cc=kernel-team@android.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=minchan@kernel.org \
--cc=oleg@redhat.com \
--cc=riel@surriel.com \
--cc=rientjes@google.com \
--cc=shakeelb@google.com \
--cc=surenb@google.com \
--cc=timmurray@google.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).