On Fri 17-03-17 10:50:20, Johannes Weiner wrote: > On Wed, Mar 15, 2017 at 07:36:48PM +0800, Yisheng Xie wrote: > > By reviewing code, I find that when enter do_try_to_free_pages, the > > may_thrash is always clear, and it will retry shrink zones to tap > > cgroup's reserves memory by setting may_thrash when the former > > shrink_zones reclaim nothing. > > > > However, when memcg is disabled or on legacy hierarchy, or there do not > > have any memcg protected by low limit, it should not do this useless retry > > at all, for we do not have any cgroup's reserves memory to tap, and we > > have already done hard work but made no progress. > > > > To avoid this unneeded retrying, add a new field in scan_control named > > memcg_low_protection, set it if there is any memcg protected by low limit > > and only do the retry when memcg_low_protection is set while may_thrash > > is clear. > > > > Signed-off-by: Yisheng Xie <xieyishe...@huawei.com> > > Suggested-by: Michal Hocko <mho...@kernel.org> > > Suggested-by: Shakeel Butt <shake...@google.com> > > Reviewed-by: Shakeel Butt <shake...@google.com> > > I don't see the point of this patch. It adds more code just to > marginally optimize a near-OOM cold path.
The current behavior is surprising and not really desirable when we want to control the retry logic from the page allocator. So I do not think that the additional 5 lines of code would be unbearable burden or maintenance cost. I am not saying the patch adds any break through but it is not pointless either. -- Michal Hocko SUSE Labs
