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

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Date:	Thu, 29 May 2014 17:31:42 -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 5:20 PM, Minchan Kim <minchan@...nel.org> wrote:
>
> I guess this part which avoid swapout in direct reclaim would be key
> if this patch were successful. But it could make anon pages rotate back
> into inactive's head from tail in direct reclaim path until kswapd can
> catch up. And kswapd kswapd can swap out anon pages from tail of inactive
> LRU so I suspect it could make side-effect LRU churning.

Oh, it could make bad things happen, no question about that.

That said, those bad things are what happens to shared mapped pages
today, so in that sense it's not new. But large dirty shared mmap's
have traditionally been a great way to really hurt out VM, so "it
should work as well as shared mapping pages" is definitely not a
ringing endorsement!

(Of course, *if* we can improve kswapd behavior for both swap-out and
shared dirty pages, that would then be a double win, so there is
_some_ argument for saying that we should aim to handle both kinds of
pages equally).

> Anyway, I will queue it into testing machine since Rusty's test is done.

You could also try Dave's patch, and _not_ do my mm/vmscan.c part.

            Linus
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