linux-kernel - Re: [PATCH lttng-modules 4/5] fix: mm: move recent_rotated pages calculation to shrink_inactive

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Message-ID: <bcb13b3a-44f4-c8da-ab32-2fa3e37ee81e@virtuozzo.com>
Date:   Wed, 22 May 2019 11:37:26 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Michael Jeanson <mjeanson@...icios.com>
Cc:     lttng-dev <lttng-dev@...ts.lttng.org>,
        rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH lttng-modules 4/5] fix: mm: move recent_rotated pages
 calculation to shrink_inactive_list() (v5.2)

On 21.05.2019 23:53, Mathieu Desnoyers wrote:
> ----- On May 21, 2019, at 4:33 PM, Michael Jeanson mjeanson@...icios.com wrote:
> 
>> See upstream commit:
>>
>>  commit 886cf1901db962cee5f8b82b9b260079a5e8a4eb
>>  Author: Kirill Tkhai <ktkhai@...tuozzo.com>
>>  Date:   Mon May 13 17:16:51 2019 -0700
>>
>>    mm: move recent_rotated pages calculation to shrink_inactive_list()
>>
>>    Patch series "mm: Generalize putback functions"]
>>
>>    putback_inactive_pages() and move_active_pages_to_lru() are almost
>>    similar, so this patchset merges them ina single function.
>>
>>    This patch (of 4):
>>
>>    The patch moves the calculation from putback_inactive_pages() to
>>    shrink_inactive_list().  This makes putback_inactive_pages() looking more
>>    similar to move_active_pages_to_lru().
>>
>>    To do that, we account activated pages in reclaim_stat::nr_activate.
>>    Since a page may change its LRU type from anon to file cache inside
>>    shrink_page_list() (see ClearPageSwapBacked()), we have to account pages
>>    for the both types.  So, nr_activate becomes an array.
>>
>>    Previously we used nr_activate to account PGACTIVATE events, but now we
>>    account them into pgactivate variable (since they are about number of
>>    pages in general, not about sum of hpage_nr_pages).
>>
>> Signed-off-by: Michael Jeanson <mjeanson@...icios.com>
>> ---
>> instrumentation/events/lttng-module/mm_vmscan.h | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/instrumentation/events/lttng-module/mm_vmscan.h
>> b/instrumentation/events/lttng-module/mm_vmscan.h
>> index 417472c..3f9ffde 100644
>> --- a/instrumentation/events/lttng-module/mm_vmscan.h
>> +++ b/instrumentation/events/lttng-module/mm_vmscan.h
>> @@ -625,7 +625,8 @@ LTTNG_TRACEPOINT_EVENT(mm_vmscan_lru_shrink_inactive,
>> 		ctf_integer(unsigned long, nr_writeback, stat->nr_writeback)
>> 		ctf_integer(unsigned long, nr_congested, stat->nr_congested)
>> 		ctf_integer(unsigned long, nr_immediate, stat->nr_immediate)
>> -		ctf_integer(unsigned long, nr_activate, stat->nr_activate)
>> +		ctf_integer(unsigned long, nr_activate0, stat->nr_activate[0])
>> +		ctf_integer(unsigned long, nr_activate1, stat->nr_activate[1])
> 
> This patch is for lttng-modules, but I'm adding Kirill Tkhai (author of the Linux
> kernel commit causing the need for this change in lttng-modules) and Steven Rostedt
> in CC, because I feel they might want to join this discussion naming of
> userspace-visible TRACE_EVENT() fields.
> 
> Based on the upstream Linux commit, it looks like only the TP_printk() has
> sane names for event fields, but could really improve on the naming for the
> binary version of those fields:
> 
> -       TP_printk("nid=%d nr_scanned=%ld nr_reclaimed=%ld nr_dirty=%ld nr_writeback=%ld nr_congested=%ld nr_immediate=%ld nr_activate=%ld nr_ref_keep=%ld nr_unmap_fail=%ld priority=%d flags=%s",
> +       TP_printk("nid=%d nr_scanned=%ld nr_reclaimed=%ld nr_dirty=%ld nr_writeback=%ld nr_congested=%ld nr_immediate=%ld nr_activate_anon=%d nr_activate_file=%d nr_ref_keep=%ld nr_unmap_fail=%ld priority=%d flags=%s",
>                 __entry->nid,
>                 __entry->nr_scanned, __entry->nr_reclaimed,
>                 __entry->nr_dirty, __entry->nr_writeback,
>                 __entry->nr_congested, __entry->nr_immediate,
> -               __entry->nr_activate, __entry->nr_ref_keep,
> -               __entry->nr_unmap_fail, __entry->priority,
> +               __entry->nr_activate0, __entry->nr_activate1,
> +               __entry->nr_ref_keep, __entry->nr_unmap_fail,
> +               __entry->priority,
>                 show_reclaim_flags(__entry->reclaim_flags))
>  );
> 
> So I recommend we do the following in lttng-modules:
> 
> Rename the field nr_activate0 to nr_activate_anon,
> Rename the field nr_activate1 to nr_activate_file.
> 
> So users can make something out of those tracepoints without digging
> into the kernel source code.
> 
> Even if Steven and Kirill end up choosing to change the name of those
> fields upstream in trace-event, it won't have any impact on lttng-modules.
> 
> It would make sense to change those newly introduced exposed names in the
> upstream kernel as well though.

Yeah, since these are exported to userspace, we should better rename them in the way
you suggested.

Thanks,
Kirill