From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/swap: piggyback lru_add_drain_all() calls
Date: Fri, 4 Oct 2019 15:24:43 +0300 [thread overview]
Message-ID: <d6388815-b664-d5f0-8e52-d96438408758@yandex-team.ru> (raw)
In-Reply-To: <20191004121017.GG32665@bombadil.infradead.org>
On 04/10/2019 15.10, Matthew Wilcox wrote:
> On Fri, Oct 04, 2019 at 01:11:06PM +0300, Konstantin Khlebnikov wrote:
>> This is very slow operation. There is no reason to do it again if somebody
>> else already drained all per-cpu vectors after we waited for lock.
>> + seq = raw_read_seqcount_latch(&seqcount);
>> +
>> mutex_lock(&lock);
>> +
>> + /* Piggyback on drain done by somebody else. */
>> + if (__read_seqcount_retry(&seqcount, seq))
>> + goto done;
>> +
>> + raw_write_seqcount_latch(&seqcount);
>> +
>
> Do we really need the seqcount to do this? Wouldn't a mutex_trylock()
> have the same effect?
>
No, this is completely different semantics.
Operation could be safely skipped only if somebody else started and
finished drain after current task called this function.
next prev parent reply other threads:[~2019-10-04 12:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 10:11 Konstantin Khlebnikov
2019-10-04 12:10 ` Matthew Wilcox
2019-10-04 12:24 ` Konstantin Khlebnikov [this message]
2019-10-04 12:27 ` Michal Hocko
2019-10-04 12:32 ` Konstantin Khlebnikov
2019-10-04 12:37 ` Michal Hocko
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