linux-kernel - Re: [PATCH 2/2] mm: multi-gen lru: fix stat count

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Date:   Thu, 19 Oct 2023 14:29:52 +0800
From:   Huan Yang <link@...o.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org, opensource.kernel@...o.com
Subject: Re: [PATCH 2/2] mm: multi-gen lru: fix stat count


在 2023/10/19 10:39, Yu Zhao 写道:
> On Wed, Oct 18, 2023 at 8:17 PM Huan Yang <link@...o.com> wrote:
>> Hi Yu Zhao,
>>
>> Thanks for your reply.
>>
>> 在 2023/10/19 0:21, Yu Zhao 写道:
>>> On Wed, Oct 18, 2023 at 2:22 AM Huan Yang <link@...o.com> wrote:
>>>> For multi-gen lru reclaim in evict_folios, like shrink_inactive_list,
>>>> gather folios which isolate to reclaim, and invoke shirnk_folio_list.
>>>>
>>>> But, when complete shrink, it not gather shrink reclaim stat into sc,
>>>> we can't get info like nr_dirty\congested in reclaim, and then
>>>> control writeback, dirty number and mark as LRUVEC_CONGESTED, or
>>>> just bpf trace shrink and get correct sc stat.
>>>>
>>>> This patch fix this by simple copy code from shrink_inactive_list when
>>>> end of shrink list.
>>> MGLRU doesn't try to write back dirt file pages in the reclaim path --
>>> it filters them out in sort_folio() and leaves them to the page
>> Nice to know this,  sort_folio() filters some folio indeed.
>> But, I want to know, if we touch some folio in shrink_folio_list(), may some
>> folio become dirty or writeback even if sort_folio() filter then?
> Good question: in that case MGLRU still doesn't try to write those
> folios back because isolate_folio() cleared PG_reclaim and
> shrink_folio_list() checks PG_reclaim:

Thank you too much. So, MGLRU have many diff between typic LRU reclaim.
So, why don't offer MGLRU a own shrink path to avoid so many check of folio?
And more think, it's nice to assign a anon/file reclaim hook into 
anon_vma/address_space?
(Each folio, have their own shrink path, don't try check path if it no 
need.)

>
> if (folio_test_dirty(folio)) {
> /*
> * Only kswapd can writeback filesystem folios
> * to avoid risk of stack overflow. But avoid
> * injecting inefficient single-folio I/O into
> * flusher writeback as much as possible: only
> * write folios when we've encountered many
> * dirty folios, and when we've already scanned
> * the rest of the LRU for clean folios and see
> * the same dirty folios again (with the reclaim
> * flag set).
> */
> if (folio_is_file_lru(folio) &&
>      (!current_is_kswapd() ||
>       !folio_test_reclaim(folio) ||
>       !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
Thanks