On Thu, Nov 10, 2011 at 10:06:16AM +0000, Mel Gorman wrote:
> than stall. It was suggested that __GFP_NORETRY be used instead of
> __GFP_NO_KSWAPD. This would look less like a special case but would
> still cause compaction to run at least once with sync compaction.
>
This comment is bogus - __GFP_NORETRY would have caught THP allocations
and would not call sync compaction. The issue was that it would also
have caught any hypothetical high-order GFP_THISNODE allocations that
end up calling compaction here
/*
* High-order allocations do not necessarily loop after
* direct reclaim and reclaim/compaction depends on
* compaction being called after reclaim so call directly if
* necessary
*/
page = __alloc_pages_direct_compact(gfp_mask, order,
zonelist, high_zoneidx,
nodemask,
alloc_flags, preferred_zone,
migratetype, &did_some_progress,
sync_migration);
__GFP_NORETRY is used in a bunch of places and while the most
of them are not high-order, some of them potentially are like in
sound/core/memalloc.c. Using __GFP_NO_KSWAPD as the flag allows
these callers to continue using sync compaction. It could be argued
that they would prefer __GFP_NORETRY but the potential side-effects
should be taken should be taken into account and the comment updated
if that happens.
--
Mel Gorman
SUSE Labs
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