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Date: Tue, 24 Nov 2020 12:21:28 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Alex Shi <alex.shi@...ux.alibaba.com>,
Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
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 11/22/20 3:00 PM, Alex Shi wrote:
> Thanks a lot for all comments, I picked all up and here is the v3:
>
> From 167131dd106a96fd08af725df850e0da6ec899af Mon Sep 17 00:00:00 2001
> From: Alex Shi <alex.shi@...ux.alibaba.com>
> Date: Fri, 20 Nov 2020 14:49:16 +0800
> Subject: [PATCH v3 next] mm/vmscan: __isolate_lru_page_prepare clean up
>
> The function just return 2 results, so use a 'switch' to deal with its
> result is unnecessary, and simplify it to a bool func as Vlastimil
> suggested.
>
> Also remove 'goto' by reusing list_move(), and take Matthew Wilcox's
> suggestion to update comments in function.
I wouldn't mind if the goto stayed, but it's not repeating that much
without it (list_move() + continue, 3 times) so...
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Yu Zhao <yuzhao@...gle.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> ---
> include/linux/swap.h | 2 +-
> mm/compaction.c | 2 +-
> mm/vmscan.c | 68 ++++++++++++++++++++------------------------
> 3 files changed, 33 insertions(+), 39 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 596bc2f4d9b0..5bba15ac5a2e 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -356,7 +356,7 @@ extern void lru_cache_add_inactive_or_unevictable(struct page *page,
> extern unsigned long zone_reclaimable_pages(struct zone *zone);
> extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> gfp_t gfp_mask, nodemask_t *mask);
> -extern int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode);
> +extern bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode);
> extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> unsigned long nr_pages,
> gfp_t gfp_mask,
> diff --git a/mm/compaction.c b/mm/compaction.c
> index b68931854253..8d71ffebe6cb 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -988,7 +988,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> if (unlikely(!get_page_unless_zero(page)))
> goto isolate_fail;
>
> - if (__isolate_lru_page_prepare(page, isolate_mode) != 0)
> + if (!__isolate_lru_page_prepare(page, isolate_mode))
> goto isolate_fail_put;
>
> /* Try isolate the page */
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c6f94e55c3fe..4d2703c43310 100644
> --- a/mm/vmscan.c
> +++ 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 true on success, false on failure.
> */
> -int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
> +bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
> {
> - int ret = -EBUSY;
> -
> /* Only take pages on the LRU. */
> if (!PageLRU(page))
> - return ret;
> + return false;
>
> /* Compaction should not handle unevictable pages but CMA can do so */
> if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
> - return ret;
> + return false;
>
> /*
> * To minimise LRU disruption, the caller can indicate that it only
> @@ -1561,7 +1559,7 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
> if (mode & ISOLATE_ASYNC_MIGRATE) {
> /* All the caller can do on PageWriteback is block */
> if (PageWriteback(page))
> - return ret;
> + return false;
>
> if (PageDirty(page)) {
> struct address_space *mapping;
> @@ -1577,20 +1575,20 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
> * from the page cache.
> */
> if (!trylock_page(page))
> - return ret;
> + return false;
>
> mapping = page_mapping(page);
> migrate_dirty = !mapping || mapping->a_ops->migratepage;
> unlock_page(page);
> if (!migrate_dirty)
> - return ret;
> + return false;
> }
> }
>
> if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
> - return ret;
> + return false;
>
> - return 0;
> + return true;
> }
>
> /*
> @@ -1674,35 +1672,31 @@ 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:
> - /*
> - * Be careful not to clear PageLRU until after we're
> - * sure the page is not being freed elsewhere -- the
> - * page release code relies on it.
> - */
> - if (unlikely(!get_page_unless_zero(page)))
> - goto busy;
> -
> - if (!TestClearPageLRU(page)) {
> - /*
> - * This page may in other isolation path,
> - * but we still hold lru_lock.
> - */
> - put_page(page);
> - goto busy;
> - }
> -
> - nr_taken += nr_pages;
> - nr_zone_taken[page_zonenum(page)] += nr_pages;
> - list_move(&page->lru, dst);
> - break;
> + if (!__isolate_lru_page_prepare(page, mode)) {
> + /* It is being freed elsewhere */
> + list_move(&page->lru, src);
> + continue;
> + }
> + /*
> + * Be careful not to clear PageLRU until after we're
> + * sure the page is not being freed elsewhere -- the
> + * page release code relies on it.
> + */
> + if (unlikely(!get_page_unless_zero(page))) {
> + list_move(&page->lru, src);
> + continue;
> + }
>
> - default:
> -busy:
> - /* else it is being freed elsewhere */
> + if (!TestClearPageLRU(page)) {
> + /* Another thread is already isolating this page */
> + put_page(page);
> list_move(&page->lru, src);
> + continue;
> }
> +
> + nr_taken += nr_pages;
> + nr_zone_taken[page_zonenum(page)] += nr_pages;
> + list_move(&page->lru, dst);
> }
>
> /*
>
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