netdev - Re: ppoll() stuck on POLLIN while TCP peer is sending

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Message-ID: <20130109212907.GA27361@dcvr.yhbt.net>
Date:	Wed, 9 Jan 2013 21:29:07 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Mel Gorman <mgorman@...e.de>
Cc:	linux-mm@...ck.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: ppoll() stuck on POLLIN while TCP peer is sending

Mel Gorman <mgorman@...e.de> wrote:
> When I looked at it for long enough I found a number of problems. Most
> affect timing but two serious issues are in there. One affects how long
> kswapd spends compacting versus reclaiming and the other increases lock
> contention meaning that async compaction can abort early. Both are serious
> and could explain why a driver would fail high-order allocations.
> 
> Please try the following patch. However, even if it works the benefit of
> capture may be so marginal that partially reverting it and simplifying
> compaction.c is the better decision.

Btw, I'm still testing this patch with the "page->pfemalloc = false"
change on top of it.

> diff --git a/mm/compaction.c b/mm/compaction.c
> index 6b807e4..03c82c0 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -857,7 +857,8 @@ static int compact_finished(struct zone *zone,
>  	} else {
>  		unsigned int order;
>  		for (order = cc->order; order < MAX_ORDER; order++) {
> -			struct free_area *area = &zone->free_area[cc->order];
> +			struct free_area *area = &zone->free_area[order];

I noticed something like this hunk wasn't in your latest partial revert
(<20130109135010.GB13475@...e.de>)
I admit I don't understand this code, but this jumped out at me.
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