ppoll() stuck on POLLIN while TCP peer is sending

On Tue, Jan 08, 2013 at 11:23:25PM +0000, Eric Wong wrote:
> Mel Gorman <mgorman@suse.de> wrote:
> > 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.
> 
> I already got my VM stuck on this one.  I had two twosleepy instances,
> 2774 was the one that got stuck (also confirmed by watching top).
> 

page->pfmemalloc can be left set for captured pages so try this but as
capture is rarely used I'm strongly favouring a partial revert even if
this works for you. I haven't reproduced this using your workload yet
but I have found that high-order allocation stress tests for 3.8-rc2 are
completely screwed. 71% success rates at rest in 3.7 and 6% in 3.8-rc2 so
I have to chase that down too.

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Mel Gorman <mgorman@suse.de> wrote:
> page->pfmemalloc can be left set for captured pages so try this but as
> capture is rarely used I'm strongly favouring a partial revert even if
> this works for you. I haven't reproduced this using your workload yet
> but I have found that high-order allocation stress tests for 3.8-rc2 are
> completely screwed. 71% success rates at rest in 3.7 and 6% in 3.8-rc2 so
> I have to chase that down too.
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9d20c13..c242d21 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2180,8 +2180,10 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
>  	current->flags &= ~PF_MEMALLOC;
>  
>  	/* If compaction captured a page, prep and use it */
> -	if (page && !prep_new_page(page, order, gfp_mask))
> +	if (page && !prep_new_page(page, order, gfp_mask)) {
> +		page->pfmemalloc = false;
>  		goto got_page;
> +	}
>  
>  	if (*did_some_progress != COMPACT_SKIPPED) {
>  		/* Page migration frees to the PCP lists but we want merging */

This (on top of your previous patch) seems to work great after several
hours of testing on both my VM and real machine.  I haven't tried your
partial revert, yet.  Will try that in a bit on the VM.
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