linux-kernel - Re: [PATCH] mm/swap: piggyback lru_add_drain

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20191004121017.GG32665@bombadil.infradead.org>
Date:   Fri, 4 Oct 2019 05:10:17 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/swap: piggyback lru_add_drain_all() calls

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?