Re: [PATCH next] mm/vmscan: __isolate_lru_page_prepare clean up

[Matthew Wilcox <willy@infradead.org>]

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;
>  		}