Re: [PATCH RFC] delayacct: add memory reclaim delay in get_page_from_freelist

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 31 Aug 2023 07:26:20 +0000 "liwenyu01@bilibili.com" <liwenyu01@bilibili.com> wrote:

> reclaim of the task in do_try_to_free_pages(). In systems with NUMA
> open, some tasks occasionally experience slower response times, but the
> total count of reclaim does not increase, using ftrace can show that
> node_reclaim has occurred.
> 
> The memory reclaim occurring in get_page_from_freelist() is also due to
> heavy memory load. To get the impact of tasks in memory reclaim, this
> patch adds the statistics of the memory reclaim delay statistics for
> __node_reclaim().
> 
> ...
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -8010,6 +8010,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
> 
>         cond_resched();
>         psi_memstall_enter(&pflags);
> +       delayacct_freepages_start();
>         fs_reclaim_acquire(sc.gfp_mask);
>         /*
>          * We need to be able to allocate from the reserves for RECLAIM_UNMAP
> @@ -8032,6 +8033,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
>         memalloc_noreclaim_restore(noreclaim_flag);
>         fs_reclaim_release(sc.gfp_mask);
>         psi_memstall_leave(&pflags);
> +       delayacct_freepages_end();
> 
>         trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);

__node_reclaim() calls shrink_node() which at some point will call
do_try_to_free_pages() (yes?), which calls delayacct_freepages_start().

So we're effectively nesting calls to delayacct_freepages_start(),
which isn't designed for that?