Re: [PATCH 3/8] mm, page_alloc: don't retry initial attempt in slowpath

[Vlastimil Babka]

On 07/18/2016 01:29 PM, Michal Hocko wrote:
> On Mon 18-07-16 13:22:57, Vlastimil Babka wrote:
> > After __alloc_pages_slowpath() sets up new alloc_flags and wakes up kswapd, it
> > first tries get_page_from_freelist() with the new alloc_flags, as it may
> > succeed e.g. due to using min watermark instead of low watermark. It makes
> > sense to to do this attempt before adjusting zonelist based on
> > alloc_flags/gfp_mask, as it's still relatively a fast path if we just wake up
> > kswapd and successfully allocate.
> >
> > This patch therefore moves the initial attempt above the retry label and
> > reorganizes a bit the part below the retry label. We still have to attempt
> > get_page_from_freelist() on each retry, as some allocations cannot do that
> > as part of direct reclaim or compaction, and yet are not allowed to fail
> > (even though they do a WARN_ON_ONCE() and thus should not exist). We can reuse
> > the call meant for ALLOC_NO_WATERMARKS attempt and just set alloc_flags to
> > ALLOC_NO_WATERMARKS if the context allows it. As a side-effect, the attempts
> > from direct reclaim/compaction will also no longer obey watermarks once this
> > is set, but there's little harm in that.
> >
> > Kswapd wakeups are also done on each retry to be safe from potential races
> > resulting in kswapd going to sleep while a process (that may not be able to
> > reclaim by itself) is still looping.
> >
> > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> Same here, my ack still holds
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Sorry, forgot to add them before sending. Thanks for both!