linux-kernel - Re: [RFC 2/2] x86_64: expand kernel stack to 16K

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Date:	Thu, 29 May 2014 17:05:17 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K

On Thu, May 29, 2014 at 4:36 PM, Minchan Kim <minchan@...nel.org> wrote:
>
> I did below hacky test to apply your idea and the result is overflow again.
> So, again it would second stack expansion. Otherwise, we should prevent
> swapout in direct reclaim.

So changing io_schedule() is bad, for the reasons I outlined elsewhere
(we use it for wait_for_page*() - see sleep_on_page().

It's the congestion waiting where the io_schedule() should be avoided.

So maybe test a patch something like the attached.

NOTE! This is absolutely TOTALLY UNTESTED! It might do horrible
horrible things. It seems to compile, but I have absolutely no reason
to believe that it would work. I didn't actually test that this moves
anything at all to kblockd. So think of it as a concept patch that
*might* work, but as Dave said, there might also be other things that
cause unplugging and need some tough love.

                   Linus

View attachment "patch.diff" of type "text/plain" (2753 bytes)