From: Minchan Kim <minchan@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <js1304@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Nazarewicz <mina86@mina86.com>,
Mel Gorman <mgorman@suse.de>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation
Date: Thu, 19 Nov 2015 15:50:15 +0900 [thread overview]
Message-ID: <20151119065015.GB15540@bbox> (raw)
In-Reply-To: <564C9A86.1090906@suse.cz>
On Wed, Nov 18, 2015 at 04:34:30PM +0100, Vlastimil Babka wrote:
> On 11/09/2015 08:23 AM, Joonsoo Kim wrote:
> > CMA allocation should be guaranteed to succeed by definition, but,
> > unfortunately, it would be failed sometimes. It is hard to track down
> > the problem, because it is related to page reference manipulation and
> > we don't have any facility to analyze it.
>
> Reminds me of the PeterZ's VM_PINNED patchset. What happened to it?
> https://lwn.net/Articles/600502/
>
> > This patch adds tracepoints to track down page reference manipulation.
> > With it, we can find exact reason of failure and can fix the problem.
> > Following is an example of tracepoint output.
> >
> > <...>-9018 [004] 92.678375: page_ref_set: pfn=0x17ac9 flags=0x0 count=1 mapcount=0 mapping=(nil) mt=4 val=1
> > <...>-9018 [004] 92.678378: kernel_stack:
> > => get_page_from_freelist (ffffffff81176659)
> > => __alloc_pages_nodemask (ffffffff81176d22)
> > => alloc_pages_vma (ffffffff811bf675)
> > => handle_mm_fault (ffffffff8119e693)
> > => __do_page_fault (ffffffff810631ea)
> > => trace_do_page_fault (ffffffff81063543)
> > => do_async_page_fault (ffffffff8105c40a)
> > => async_page_fault (ffffffff817581d8)
> > [snip]
> > <...>-9018 [004] 92.678379: page_ref_mod: pfn=0x17ac9 flags=0x40048 count=2 mapcount=1 mapping=0xffff880015a78dc1 mt=4 val=1
> > [snip]
> > ...
> > ...
> > <...>-9131 [001] 93.174468: test_pages_isolated: start_pfn=0x17800 end_pfn=0x17c00 fin_pfn=0x17ac9 ret=fail
> > [snip]
> > <...>-9018 [004] 93.174843: page_ref_mod_and_test: pfn=0x17ac9 flags=0x40068 count=0 mapcount=0 mapping=0xffff880015a78dc1 mt=4 val=-1 ret=1
> > => release_pages (ffffffff8117c9e4)
> > => free_pages_and_swap_cache (ffffffff811b0697)
> > => tlb_flush_mmu_free (ffffffff81199616)
> > => tlb_finish_mmu (ffffffff8119a62c)
> > => exit_mmap (ffffffff811a53f7)
> > => mmput (ffffffff81073f47)
> > => do_exit (ffffffff810794e9)
> > => do_group_exit (ffffffff81079def)
> > => SyS_exit_group (ffffffff81079e74)
> > => entry_SYSCALL_64_fastpath (ffffffff817560b6)
> >
> > This output shows that problem comes from exit path. In exit path,
> > to improve performance, pages are not freed immediately. They are gathered
> > and processed by batch. During this process, migration cannot be possible
> > and CMA allocation is failed. This problem is hard to find without this
> > page reference tracepoint facility.
>
> Yeah but when you realized it was this problem, what was the fix? Probably not
> remove batching from exit path? Shouldn't CMA in this case just try waiting for
> the pins to go away, which would eventually happen? And for long-term pins,
> VM_PINNED would make sure the pages are migrated away from CMA pageblocks first?
>
> So I'm worried that this is quite nontrivial change for a very specific usecase.
This patch is not to solve the problem but just to expose what is culprit.
For using VM_PINNED, firstly, we should know where are long-term pins.
There are obviously clear places which will be first target if we use
VM_PINNED but somewhere are vague. For vague places, this patch will
help finding there. Even we don't use VM_PINNED, this patch will expose
current obstacle which can help to understand current problems.
next prev parent reply other threads:[~2015-11-19 6:50 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-09 7:23 [PATCH 1/2] mm: introduce page reference manipulation functions Joonsoo Kim
2015-11-09 7:23 ` [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation Joonsoo Kim
2015-11-10 16:02 ` Michal Nazarewicz
2015-11-18 15:34 ` Vlastimil Babka
2015-11-19 6:50 ` Minchan Kim [this message]
2015-11-20 6:33 ` Joonsoo Kim
2015-11-20 16:42 ` Steven Rostedt
2015-11-23 8:28 ` Joonsoo Kim
2015-11-23 14:26 ` Steven Rostedt
2015-11-24 1:45 ` Joonsoo Kim
2015-12-03 4:16 ` Joonsoo Kim
2015-12-09 20:01 ` Steven Rostedt
2015-12-10 2:50 ` Joonsoo Kim
2015-12-10 3:36 ` Steven Rostedt
2015-12-10 4:07 ` Joonsoo Kim
2015-11-24 1:56 ` Joonsoo Kim
2015-11-09 7:53 ` [PATCH 1/2] mm: introduce page reference manipulation functions Sergey Senozhatsky
2015-11-09 8:00 ` Joonsoo Kim
2015-11-09 11:45 ` Kirill A. Shutemov
2015-11-10 0:28 ` Joonsoo Kim
2015-11-10 15:58 ` Michal Nazarewicz
2016-02-15 3:04 js1304
2016-02-15 3:04 ` [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation js1304
2016-02-15 5:08 ` Sergey Senozhatsky
2016-02-15 5:28 ` Sergey Senozhatsky
2016-02-15 14:18 ` Joonsoo Kim
2016-02-15 16:07 ` Steven Rostedt
2016-02-16 0:47 ` Joonsoo Kim
2016-02-16 1:16 ` Steven Rostedt
2016-02-18 7:46 ` Joonsoo Kim
2016-02-18 14:20 ` Steven Rostedt
2016-02-18 14:29 ` Steven Rostedt
2016-02-19 0:34 ` Sergey Senozhatsky
2016-02-19 1:39 ` Joonsoo Kim
2016-02-19 1:46 ` Steven Rostedt
2016-02-19 2:15 ` Sergey Senozhatsky
2016-02-19 1:20 ` Joonsoo Kim
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