linux-kernel - Re: [PATCH v18 22/32] mm/vmscan: use relock for move_pages_to

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Message-ID: <alpine.LSU.2.11.2009212240370.6434@eggly.anvils>
Date:   Mon, 21 Sep 2020 22:44:16 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
cc:     akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        tj@...nel.org, hughd@...gle.com, khlebnikov@...dex-team.ru,
        daniel.m.jordan@...cle.com, willy@...radead.org,
        hannes@...xchg.org, lkp@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        shakeelb@...gle.com, iamjoonsoo.kim@....com,
        richard.weiyang@...il.com, kirill@...temov.name,
        alexander.duyck@...il.com, rong.a.chen@...el.com, mhocko@...e.com,
        vdavydov.dev@...il.com, shy828301@...il.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v18 22/32] mm/vmscan: use relock for move_pages_to_lru

On Mon, 24 Aug 2020, Alex Shi wrote:

> From: Hugh Dickins <hughd@...gle.com>
> 
> Use the relock function to replace relocking action. And try to save few
> lock times.
> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
> Reviewed-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>

NAK. Who wrote this rubbish? Oh, did I? Maybe something you extracted
from my tarball. No, we don't need any of this now, as explained when
going through 20/32.

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: cgroups@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mm@...ck.org
> ---
>  mm/vmscan.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2c94790d4cb1..04ef94190530 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1848,15 +1848,15 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  	enum lru_list lru;
>  
>  	while (!list_empty(list)) {
> -		struct lruvec *new_lruvec = NULL;
> -
>  		page = lru_to_page(list);
>  		VM_BUG_ON_PAGE(PageLRU(page), page);
>  		list_del(&page->lru);
>  		if (unlikely(!page_evictable(page))) {
> -			spin_unlock_irq(&lruvec->lru_lock);
> +			if (lruvec) {
> +				spin_unlock_irq(&lruvec->lru_lock);
> +				lruvec = NULL;
> +			}
>  			putback_lru_page(page);
> -			spin_lock_irq(&lruvec->lru_lock);
>  			continue;
>  		}
>  
> @@ -1871,12 +1871,7 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  		 *     list_add(&page->lru,)
>  		 *                                        list_add(&page->lru,)
>  		 */
> -		new_lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
> -		if (new_lruvec != lruvec) {
> -			if (lruvec)
> -				spin_unlock_irq(&lruvec->lru_lock);
> -			lruvec = lock_page_lruvec_irq(page);
> -		}
> +		lruvec = relock_page_lruvec_irq(page, lruvec);
>  		SetPageLRU(page);
>  
>  		if (unlikely(put_page_testzero(page))) {
> @@ -1885,8 +1880,8 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  
>  			if (unlikely(PageCompound(page))) {
>  				spin_unlock_irq(&lruvec->lru_lock);
> +				lruvec = NULL;
>  				destroy_compound_page(page);
> -				spin_lock_irq(&lruvec->lru_lock);
>  			} else
>  				list_add(&page->lru, &pages_to_free);
>  
> -- 
> 1.8.3.1