[lkml]   [2017]   [Aug]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 1/2] sched/wait: Break up long wake list walk
On 08/18/2017 07:46 AM, Mel Gorman wrote:
> On Fri, Aug 18, 2017 at 02:20:38PM +0000, Liang, Kan wrote:
>>> Nothing fancy other than needing a comment if it works.
>> No, the patch doesn't work.
> That indicates that it may be a hot page and it's possible that the page is
> locked for a short time but waiters accumulate. What happens if you leave
> NUMA balancing enabled but disable THP? Waiting on migration entries also
> uses wait_on_page_locked so it would be interesting to know if the problem
> is specific to THP.
> Can you tell me what this workload is doing? I want to see if it's something
> like many threads pounding on a limited number of pages very quickly. If

It is a customer workload so we have limited visibility. But we believe there are
some pages that are frequently accessed by all threads.

> it's many threads working on private data, it would also be important to
> know how each buffers threads are aligned, particularly if the buffers
> are smaller than a THP or base page size. For example, if each thread is
> operating on a base page sized buffer then disabling THP would side-step
> the problem but THP would be false sharing between multiple threads.

Still, I don't think this problem is THP specific. If there is a hot
regular page getting migrated, we'll also see many threads get
queued up quickly. THP may have made the problem worse as migrating
it takes a longer time, meaning more threads could get queued up.



 \ /
  Last update: 2017-08-18 18:36    [W:0.085 / U:10.268 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site