linux-kernel - Re: [PATCH next] mm/vmscan: __isolate_lru_page

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Message-ID: <20201122123552.GF4327@casper.infradead.org>
Date:   Sun, 22 Nov 2020 12:35:52 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] mm/vmscan: __isolate_lru_page_prepare clean up

On Sun, Nov 22, 2020 at 08:00:19PM +0800, Alex Shi wrote:
>  mm/compaction.c |  2 +-
>  mm/vmscan.c     | 69 +++++++++++++++++++++++--------------------------
>  2 files changed, 34 insertions(+), 37 deletions(-)

How is it possible you're changing the signature of a function without
touching a header file?  Surely __isolate_lru_page_prepare() must be declared
in mm/internal.h ?

> +++ b/mm/vmscan.c
> @@ -1536,19 +1536,17 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
>   * page:	page to consider
>   * mode:	one of the LRU isolation modes defined above
>   *
> - * returns 0 on success, -ve errno on failure.
> + * returns ture on success, false on failure.

"true".

> @@ -1674,35 +1672,34 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  		 * only when the page is being freed somewhere else.
>  		 */
>  		scan += nr_pages;
> -		switch (__isolate_lru_page_prepare(page, mode)) {
> -		case 0:
> +		if (!__isolate_lru_page_prepare(page, mode)) {
> +			/* else it is being freed elsewhere */

I don't think the word "else" helps here.  Just
			/* It is being freed elsewhere */

> +		if (!TestClearPageLRU(page)) {
>  			/*
> +			 * This page may in other isolation path,
> +			 * but we still hold lru_lock.
>  			 */

I don't think this comment helps me understand what's going on here.
Maybe:

			/* Another thread is already isolating this page */

> +			put_page(page);
>  			list_move(&page->lru, src);
> +			continue;
>  		}