Re: [patch] mm: move pagevec stripping to save unlock-relock

[MinChan Kim]

Nice catch!

Reviewed-by: MinChan Kim <minchan.kim@xxxxxxxxx>

On Wed, Feb 25, 2009 at 11:38 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> In shrink_active_list() after the deactivation loop, we strip buffer
> heads from the potentially remaining pages in the pagevec.
>
> Currently, this drops the zone's lru lock for stripping, only to
> reacquire it again afterwards to update statistics.
>
> It is not necessary to strip the pages before updating the stats, so
> move the whole thing out of the protected region and save the extra
> locking.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> Âmm/vmscan.c | Â Â7 ++-----
> Â1 file changed, 2 insertions(+), 5 deletions(-)
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1298,14 +1298,11 @@ static void shrink_active_list(unsigned
> Â Â Â Â}
> Â Â Â Â__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
> Â Â Â Âpgdeactivate += pgmoved;
> - Â Â Â if (buffer_heads_over_limit) {
> - Â Â Â Â Â Â Â spin_unlock_irq(&zone->lru_lock);
> - Â Â Â Â Â Â Â pagevec_strip(&pvec);
> - Â Â Â Â Â Â Â spin_lock_irq(&zone->lru_lock);
> - Â Â Â }
> Â Â Â Â__count_zone_vm_events(PGREFILL, zone, pgscanned);
> Â Â Â Â__count_vm_events(PGDEACTIVATE, pgdeactivate);
> Â Â Â Âspin_unlock_irq(&zone->lru_lock);
> + Â Â Â if (buffer_heads_over_limit)
> + Â Â Â Â Â Â Â pagevec_strip(&pvec);
> Â Â Â Âif (vm_swap_full())
> Â Â Â Â Â Â Â Âpagevec_swap_free(&pvec);
>
>
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-- 
Kinds regards,
MinChan Kim
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