Re: [PATCH v1] mm: help the ALLOC_HARDER allocation pass the watermarki when CMA on

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Wed, Apr 04, 2018 at 03:37:03PM -0700, Andrew Morton wrote:
> On Wed, 4 Apr 2018 09:31:10 +0900 Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:
> 
> > On Fri, Mar 23, 2018 at 01:04:08PM -0700, Andrew Morton wrote:
> > > On Fri, 23 Mar 2018 10:33:27 +0100 Michal Hocko <mhocko@kernel.org> wrote:
> > > 
> > > > On Fri 23-03-18 17:19:26, Zhaoyang Huang wrote:
> > > > > On Fri, Mar 23, 2018 at 4:38 PM, Michal Hocko <mhocko@kernel.org> wrote:
> > > > > > On Fri 23-03-18 15:57:32, Zhaoyang Huang wrote:
> > > > > >> For the type of 'ALLOC_HARDER' page allocation, there is an express
> > > > > >> highway for the whole process which lead the allocation reach __rmqueue_xxx
> > > > > >> easier than other type.
> > > > > >> However, when CMA is enabled, the free_page within zone_watermark_ok() will
> > > > > >> be deducted for number the pages in CMA type, which may cause the watermark
> > > > > >> check fail, but there are possible enough HighAtomic or Unmovable and
> > > > > >> Reclaimable pages in the zone. So add 'alloc_harder' here to
> > > > > >> count CMA pages in to clean the obstacles on the way to the final.
> > > > > >
> > > > > > This is no longer the case in the current mmotm tree. Have a look at
> > > > > > Joonsoo's zone movable based CMA patchset http://lkml.kernel.org/r/1512114786-5085-1-git-send-email-iamjoonsoo.kim@lge.com
> > > > > >
> > > > > Thanks for the information. However, I can't find the commit in the
> > > > > latest mainline, is it merged?
> > > > 
> > > > Not yet. It is still sitting in the mmomt tree. I am not sure what is
> > > > the merge plan but I guess it is still waiting for some review feedback.
> > > 
> > > http://lkml.kernel.org/r/20171222001113.GA1729@js1304-P5Q-DELUXE
> > > 
> > > That patchset has been floating about since December and still has
> > > unresolved issues.
> > > 
> > > Joonsoo, can you please let us know the status?
> > 
> > Hello, Andrew.
> > Sorry for a late response.
> > 
> > Today, I finally have answered the question from Michal and it seems
> > that there is no problem at all.
> > 
> > http://lkml.kernel.org/r/CAAmzW4NGv7RyCYyokPoj4aR3ySKub4jaBZ3k=pt_YReFbByvsw@mail.gmail.com
> > 
> > You can merge the patch as is.
> > 
> 
> hm.
> 
> There was also a performance regression reported:
> http://lkml.kernel.org/r/20180102063528.GG30397@yexl-desktop

I analyze the report and may find the reason.

When we uses more zones, min_free_kbytes is increased for avoiding
fragmentation if THP is enabled. This patch uses one more zone to
manage CMA memory so min_free_kbytes and thus min_watermark is increased.
It would reduce our usable memory and cause regression.

However, this reservation for fragmentation isn't needed for
ZONE_MOVABLE since it has only movable pages so I send a patch to fix it.

http://lkml.kernel.org/r/<1522913236-15776-1-git-send-email-iamjoonsoo.kim@lge.com>

I'm not sure that it is a root cause of above performance regression
but I highly anticipate that they are related. I will ask the reporter
to test this patch on top of that.

Thanks.