linux-kernel - Re: fadvise interferes with readahead

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Tue, 20 Nov 2012 12:05:02 -0300
From:	Claudio Freire <klaussfreire@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	linux-kernel@...r.kernel.org,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: fadvise interferes with readahead

On Tue, Nov 20, 2012 at 11:58 AM, Fengguang Wu <fengguang.wu@...el.com> wrote:
>
>> But if cache hits were to simply update
>> readahead state, it would only mean that read calls behave the same
>> regardless of fadvise calls. I think that's worth pursuing.
>
> Here you are describing an alternative solution that will somehow trap
> into the readahead code even when, for example, the application is
> accessing once and again an already cached file?  I'm afraid this will
> add non-trivial overheads and is less attractive than the "readahead
> on fadvise" solution.

Not for all cache hits, only those in state !PageUptodate, which are
I/O in progress, the case that hurts.

>> I ought to try to prepare a patch for this to illustrate my point. Not
>> sure I'll be able to though.
>
> I'd be glad to materialize the readahead on fadvise proposal, if there
> are no obvious negative examples/cases.

I don't expect a significant performance hit if only !PageUptodate
hits invoke readahead code. But I'm no kernel expert either.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/