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Date: Wed, 28 May 2014 15:42:18 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Dave Chinner <david@fromorbit.com>
CC: Steven Rostedt <rostedt@goodmis.org>, Minchan Kim <minchan@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Hugh Dickins <hughd@google.com>, rusty@rustcorp.com.au, mst@redhat.com,
        Dave Hansen <dave.hansen@intel.com>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K
References: <1401260039-18189-1-git-send-email-minchan@kernel.org> <1401260039-18189-2-git-send-email-minchan@kernel.org> <20140528101401.43853563@gandalf.local.home> <f00f9b56-704d-4d03-ad0e-ec3ba2d122fd@email.android.com> <20140528221118.GN8554@dastard>
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On 05/28/2014 03:11 PM, Dave Chinner wrote:
> On Wed, May 28, 2014 at 07:23:23AM -0700, H. Peter Anvin wrote:
>> We tried for 4K on x86-64, too, for b quite a while as I recall.
>> The kernel stack is a one of the main costs for a thread.  I would
>> like to decouple struct thread_info from the kernel stack (PJ
>> Waskewicz was working on that before he left Intel) but that
>> doesn't buy us all that much.
>>
>> 8K additional per thread is a huge hit.  XFS has indeed always
>> been a canary, or troublespot, I suspect because it originally
>> came from another kernel where this was not an optimization
>> target.
> 
> <sigh>
> 
> Always blame XFS for stack usage problems.
> 
> Even when the reported problem is from IO to an ext4 filesystem.
> 

You were the one calling it a canary.

	-hpa