From: Uladzislau Rezki <urezki@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Uladzislau Rezki <urezki@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Nicholas Piggin <npiggin@gmail.com>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Subject: Re: [PATCH v2 1/1] mm/vmalloc: Move draining areas out of caller context
Date: Tue, 25 Jan 2022 20:17:40 +0100 [thread overview]
Message-ID: <YfBM1IF9maxuAAcL@pc638.lan> (raw)
In-Reply-To: <YfBFi5IqC0MtLADf@casper.infradead.org>
On Tue, Jan 25, 2022 at 06:46:35PM +0000, Matthew Wilcox wrote:
> On Tue, Jan 25, 2022 at 06:12:48PM +0100, Uladzislau Rezki wrote:
> > On Tue, Jan 25, 2022 at 04:50:14PM +0000, Matthew Wilcox wrote:
> > > On Tue, Jan 25, 2022 at 05:39:12PM +0100, Uladzislau Rezki (Sony) wrote:
> > > > @@ -1768,7 +1776,8 @@ static void free_vmap_area_noflush(struct vmap_area *va)
> > > >
> > > > /* After this point, we may free va at any time */
> > > > if (unlikely(nr_lazy > lazy_max_pages()))
> > > > - try_purge_vmap_area_lazy();
> > > > + if (!atomic_xchg(&drain_vmap_work_in_progress, 1))
> > > > + schedule_work(&drain_vmap_work);
> > > > }
> > >
> > > Is it necessary to have drain_vmap_work_in_progress? The documentation
> > > says:
> > >
> > > * This puts a job in the kernel-global workqueue if it was not already
> > > * queued and leaves it in the same position on the kernel-global
> > > * workqueue otherwise.
> > >
> > > and the implementation seems to use test_and_set_bit() to ensure this
> > > is true.
> > >
> > It checks pending state, if the work is in run-queue you can place it
> > one more time. The motivation of having it is to prevent the drain work
> > of being placed several times at once what i see on my stress testing.
> >
> > CPU_1: invokes vfree() -> queues the drain work -> TASK_RUNNING
> > CPU_2: invokes vfree() -> queues the drain work one more time since it was not pending
>
> But why not unconditionally call schedule_work() here?
>
We can :) The question is do we agree that extra queuing will be kind of
spurious? Because the CPU_1 will complete all cleanups once it is physically
on CPU and others workers just bail out.
We can disregard those spurious wake-ups for sure. If someone complains about
it in the future we can think later then.
Re-spin and do it unconditionally? I do not have a strong opinion about it.
--
Vlad Rezki
prev parent reply other threads:[~2022-01-25 19:18 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-25 16:39 [PATCH v2 1/1] mm/vmalloc: Move draining areas out of caller context Uladzislau Rezki (Sony)
2022-01-25 16:50 ` Matthew Wilcox
2022-01-25 17:12 ` Uladzislau Rezki
2022-01-25 18:46 ` Matthew Wilcox
2022-01-25 19:17 ` Uladzislau Rezki [this message]
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=YfBM1IF9maxuAAcL@pc638.lan \
--to=urezki@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=hch@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=npiggin@gmail.com \
--cc=oleksiy.avramchenko@sonymobile.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).