linux-kernel - Re: [RFC] scripts: Include postprocessing script for memory allocation tracing

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Date:   Mon, 12 Sep 2016 14:16:35 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Janani Ravichandran <janani.rvchndrn@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, riel@...riel.com,
        akpm@...ux-foundation.org, vdavydov@...tuozzo.com, vbabka@...e.cz,
        mgorman@...hsingularity.net, rostedt@...dmis.org
Subject: Re: [RFC] scripts: Include postprocessing script for memory
 allocation tracing

Hi,
I am sorry I didn't follow up on the previous submission. I find this
_really_ helpful. It is great that you could build on top of existing
tracepoints but one thing is not entirely clear to me. Without a begin
marker in __alloc_pages_nodemask we cannot really tell how long the
whole allocation took, which would be extremely useful. Or do you use
any graph tracer tricks to deduce that? There is a note in your
changelog but I cannot seem to find that in the changelog. And FWIW I
would be open to adding a tracepoint like that. It would make our life
so much easier...

On Sun 11-09-16 18:24:12, Janani Ravichandran wrote:
[...]
> allocation_postprocess.py is a script which reads from trace_pipe. It
> does the following to filter out info from tracepoints that may not
> be important:
> 
> 1. Displays mm_vmscan_direct_reclaim_begin and
> mm_vmscan_direct_reclaim_end only when try_to_free_pages has
> exceeded the threshold.
> 2. Displays mm_compaction_begin and mm_compaction_end only when
> compact_zone has exceeded the threshold.
> 3. Displays mm_compaction_try_to_compat_pages only when
> try_to_compact_pages has exceeded the threshold.
> 4. Displays mm_shrink_slab_start and mm_shrink_slab_end only when
> the time elapsed between them exceeds the threshold.
> 5. Displays mm_vmscan_lru_shrink_inactive only when shrink_inactive_list
> has exceeded the threshold.
> 
> When CTRL+C is pressed, the script shows the times taken by the
> shrinkers. However, currently it is not possible to differentiate among
> the
> superblock shrinkers.
> 
> Sample output:
> ^Ci915_gem_shrinker_scan : total time = 8.731000 ms, max latency =
> 0.278000 ms
> ext4_es_scan : total time = 0.970000 ms, max latency = 0.129000 ms
> scan_shadow_nodes : total time = 1.150000 ms, max latency = 0.175000 ms
> super_cache_scan : total time = 8.455000 ms, max latency = 0.466000 ms
> deferred_split_scan : total time = 25.767000 ms, max latency = 25.485000
> ms

Would it be possible to group those per the context? I mean a single
allocation/per-process drop down values rather than mixing all those
values together? For example if I see that a process is talling due to
direct reclaim I would love to see what is the worst case allocation
stall and what is the most probable source of that stall. Mixing kswapd
traces would be misleading here.

Thanks!
-- 
Michal Hocko
SUSE Labs