From:   SeongJae Park <sj@kernel.org>
To:     Baolin Wang <baolin.wang@linux.alibaba.com>
Cc:     akpm@linux-foundation.org, torvalds@linux-foundation.org,
        sj@kernel.org, hannes@cmpxchg.org, mhocko@kernel.org,
        roman.gushchin@linux.dev, shakeelb@google.com,
        muchun.song@linux.dev, naoya.horiguchi@nec.com,
        linmiaohe@huawei.com, david@redhat.com, osalvador@suse.de,
        mike.kravetz@oracle.com, willy@infradead.org,
        damon@lists.linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] mm: change to return bool for folio_isolate_lru()
Date:   Tue, 14 Feb 2023 17:46:26 +0000
Message-Id: <20230214174626.71336-1-sj@kernel.org>
In-Reply-To: <7abe2897803410fdc8f167b46bb5b0467de0e3c9.1676382188.git.baolin.wang@linux.alibaba.com>
References: 
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On Tue, 14 Feb 2023 21:59:29 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:

> Now the folio_isolate_lru() did not return a boolean value to indicate
> isolation success or not, however below code checking the return value
> can make people think that it was a boolean success/failure thing, which
> makes people easy to make mistakes (see the fix patch[1]).
> 
> if (folio_isolate_lru(folio))
> 	continue;
> 
> Thus it's better to check the negative error value expilictly returned by
> folio_isolate_lru(), which makes code more clear per Linus's suggestion[2].
> Moreover Matthew suggested we can convert the isolation functions to return
> a boolean[3], since most users did not care about the negative error value,
> and can also remove the confusing of checking return value.
> 
> So this patch converts the folio_isolate_lru() to return a boolean value,
> which means return 'true' to indicate the folio isolation is successful, and
> 'false' means a failure to isolation. Meanwhile changing all users' logic of
> checking the isolation state.
> 
> No functional changes intended.
> 
> [1] https://lore.kernel.org/all/20230131063206.28820-1-Kuan-Ying.Lee@mediatek.com/T/#u
> [2] https://lore.kernel.org/all/CAHk-=wiBrY+O-4=2mrbVyxR+hOqfdJ=Do6xoucfJ9_5az01L4Q@mail.gmail.com/
> [3] https://lore.kernel.org/all/Y+sTFqwMNAjDvxw3@casper.infradead.org/
> 
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>  mm/damon/paddr.c  |  2 +-
>  mm/folio-compat.c |  8 +++++++-
>  mm/gup.c          |  2 +-
>  mm/internal.h     |  2 +-
>  mm/khugepaged.c   |  2 +-
>  mm/madvise.c      |  4 ++--
>  mm/mempolicy.c    |  2 +-
>  mm/vmscan.c       | 10 +++++-----
>  8 files changed, 19 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index b4df9b9bcc0a..607bb69e526c 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -246,7 +246,7 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
>  
>  		folio_clear_referenced(folio);
>  		folio_test_clear_young(folio);
> -		if (folio_isolate_lru(folio)) {
> +		if (!folio_isolate_lru(folio)) {
>  			folio_put(folio);
>  			continue;
>  		}
> diff --git a/mm/folio-compat.c b/mm/folio-compat.c
> index 18c48b557926..540373cf904e 100644
> --- a/mm/folio-compat.c
> +++ b/mm/folio-compat.c
> @@ -115,9 +115,15 @@ EXPORT_SYMBOL(grab_cache_page_write_begin);
>  
>  int isolate_lru_page(struct page *page)
>  {
> +	bool ret;
> +
>  	if (WARN_RATELIMIT(PageTail(page), "trying to isolate tail page"))
>  		return -EBUSY;
> -	return folio_isolate_lru((struct folio *)page);
> +	ret = folio_isolate_lru((struct folio *)page);
> +	if (ret)
> +		return 0;
> +
> +	return -EBUSY;
>  }
>  
>  void putback_lru_page(struct page *page)
> diff --git a/mm/gup.c b/mm/gup.c
> index b0885f70579c..eab18ba045db 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1939,7 +1939,7 @@ static unsigned long collect_longterm_unpinnable_pages(
>  			drain_allow = false;
>  		}
>  
> -		if (folio_isolate_lru(folio))
> +		if (!folio_isolate_lru(folio))
>  			continue;
>  
>  		list_add_tail(&folio->lru, movable_page_list);
> diff --git a/mm/internal.h b/mm/internal.h
> index dfb37e94e140..8645e8496537 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -188,7 +188,7 @@ pgprot_t __init early_memremap_pgprot_adjust(resource_size_t phys_addr,
>   * in mm/vmscan.c:
>   */
>  int isolate_lru_page(struct page *page);
> -int folio_isolate_lru(struct folio *folio);
> +bool folio_isolate_lru(struct folio *folio);
>  void putback_lru_page(struct page *page);
>  void folio_putback_lru(struct folio *folio);
>  extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index a5d32231bfad..cee659cfa3c1 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2047,7 +2047,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
>  			goto out_unlock;
>  		}
>  
> -		if (folio_isolate_lru(folio)) {
> +		if (!folio_isolate_lru(folio)) {
>  			result = SCAN_DEL_PAGE_LRU;
>  			goto out_unlock;
>  		}
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 5a5a687d03c2..c2202f51e9dd 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -406,7 +406,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>  		folio_clear_referenced(folio);
>  		folio_test_clear_young(folio);
>  		if (pageout) {
> -			if (!folio_isolate_lru(folio)) {
> +			if (folio_isolate_lru(folio)) {
>  				if (folio_test_unevictable(folio))
>  					folio_putback_lru(folio);
>  				else
> @@ -500,7 +500,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>  		folio_clear_referenced(folio);
>  		folio_test_clear_young(folio);
>  		if (pageout) {
> -			if (!folio_isolate_lru(folio)) {
> +			if (folio_isolate_lru(folio)) {
>  				if (folio_test_unevictable(folio))
>  					folio_putback_lru(folio);
>  				else
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 0919c7a719d4..2751bc3310fd 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1033,7 +1033,7 @@ static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
>  	 * expensive, so check the estimated mapcount of the folio instead.
>  	 */
>  	if ((flags & MPOL_MF_MOVE_ALL) || folio_estimated_sharers(folio) == 1) {
> -		if (!folio_isolate_lru(folio)) {
> +		if (folio_isolate_lru(folio)) {
>  			list_add_tail(&folio->lru, foliolist);
>  			node_stat_mod_folio(folio,
>  				NR_ISOLATED_ANON + folio_is_file_lru(folio),
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 34535bbd4fe9..7658b40df947 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2337,12 +2337,12 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
>   * (2) The lru_lock must not be held.
>   * (3) Interrupts must be enabled.
>   *
> - * Return: 0 if the folio was removed from an LRU list.
> - * -EBUSY if the folio was not on an LRU list.
> + * Return: true if the folio was removed from an LRU list.
> + * false if the folio was not on an LRU list.
>   */
> -int folio_isolate_lru(struct folio *folio)
> +bool folio_isolate_lru(struct folio *folio)
>  {
> -	int ret = -EBUSY;
> +	bool ret = false;
>  
>  	VM_BUG_ON_FOLIO(!folio_ref_count(folio), folio);
>  
> @@ -2353,7 +2353,7 @@ int folio_isolate_lru(struct folio *folio)
>  		lruvec = folio_lruvec_lock_irq(folio);
>  		lruvec_del_folio(lruvec, folio);
>  		unlock_page_lruvec_irq(lruvec);
> -		ret = 0;
> +		ret = true;
>  	}
>  
>  	return ret;
> -- 
> 2.27.0

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ