linux-kernel - Re: aio: bump i_count instead of using igrab

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]

Message-ID: <x4962z12fke.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 23 Aug 2010 17:18:41 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Chris Mason <chris.mason@...cle.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: aio: bump i_count instead of using igrab

Christoph Hellwig <hch@...radead.org> writes:

> On Mon, Aug 23, 2010 at 10:47:55AM -0400, Chris Mason wrote:
>> The aio batching code is using igrab to get an extra reference on the
>> inode so it can safely batch.  igrab will go ahead and take the global
>> inode spinlock, which can be a bottleneck on large machines doing lots
>> of AIO.
>> 
>> In this case, igrab isn't required because we already have a reference
>> on the file handle.  It is safe to just bump the i_count directly
>> on the inode.
>> 
>> Benchmarking shows this patch brings IOP/s on tons of flash up by about
>> 2.5X.
>
> There's some places in XFS where we do the same, and it showed up as a
> bottle neck before.  Instead of open coding the increment we have
> a wrapper that includes and assert that the numbers is always positive.
>
> I think we really want a proper helper for general use instead of
> completly opencoding it.

Well, it would make detecting races or invalid assumptions a little
easier.  If Chris wants to code that up, that's fine with me.  Honestly,
though, I don't think it's necessary.

I've gone through the alloc/free paths for the inode and I'm convinced
this is safe.  I'm happy with this version of the patch.

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
--
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/