From: Uladzislau Rezki <urezki@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Uladzislau Rezki (Sony)" <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 18:12:48 +0100 [thread overview]
Message-ID: <YfAvkKZlVQYukays@pc638.lan> (raw)
In-Reply-To: <YfAqRrGD2UKrZHfJ@casper.infradead.org>
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
...
Instead of drain_vmap_work_in_progress hack we can make use of work_busy()
helper. The main concern with that was the comment around that function:
/**
* work_busy - test whether a work is currently pending or running
* @work: the work to be tested
*
* Test whether @work is currently pending or running. There is no
* synchronization around this function and the test result is
* unreliable and only useful as advisory hints or for debugging.
*
* Return:
* OR'd bitmask of WORK_BUSY_* bits.
*/
i am not sure how reliable this is.
Thoughts?
--
Vlad Rezki
next prev parent reply other threads:[~2022-01-25 17:19 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 [this message]
2022-01-25 18:46 ` Matthew Wilcox
2022-01-25 19:17 ` Uladzislau Rezki
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