linux-kernel - Re: [PATCH 2/2] migrate_pages_batch: code cleanup: remove is

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Message-ID: <87lehyktpv.fsf@nvidia.com>
Date:   Tue, 09 May 2023 14:33:50 +1000
From:   Alistair Popple <apopple@...dia.com>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Xin Hao <xhao@...ux.alibaba.com>,
        Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH 2/2] migrate_pages_batch: code cleanup: remove is_large


Huang Ying <ying.huang@...el.com> writes:

> Previously, in migrate_pages_batch we need to track whether the source
> folio is large/THP before splitting.  So is_large is used to cache
> folio_test_large() result.  Now, we don't need that variable any more
> because we don't count retrying and failure of large folios (only
> counting that of THP folios).  So, in this patch, is_large is removed
> to simplify the code.
>
> This is just code cleanup, no functionality changes are expected.

Reviewed-by: Alistair Popple <apopple@...dia.com>

> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Xin Hao <xhao@...ux.alibaba.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Yang Shi <shy828301@...il.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Alistair Popple <apopple@...dia.com>
> ---
>  mm/migrate.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 10709aed76d3..2ac927a82bbc 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1618,7 +1618,6 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
>  	int nr_failed = 0;
>  	int nr_retry_pages = 0;
>  	int pass = 0;
> -	bool is_large = false;
>  	bool is_thp = false;
>  	struct folio *folio, *folio2, *dst = NULL, *dst2;
>  	int rc, rc_saved = 0, nr_pages;
> @@ -1635,13 +1634,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
>  		nr_retry_pages = 0;
>  
>  		list_for_each_entry_safe(folio, folio2, from, lru) {
> -			/*
> -			 * Large folio statistics is based on the source large
> -			 * folio. Capture required information that might get
> -			 * lost during migration.
> -			 */
> -			is_large = folio_test_large(folio);
> -			is_thp = is_large && folio_test_pmd_mappable(folio);
> +			is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
>  			nr_pages = folio_nr_pages(folio);
>  
>  			cond_resched();
> @@ -1688,7 +1681,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
>  				nr_failed++;
>  				stats->nr_thp_failed += is_thp;
>  				/* Large folio NUMA faulting doesn't split to retry. */
> -				if (is_large && !nosplit) {
> +				if (folio_test_large(folio) && !nosplit) {
>  					int ret = try_split_folio(folio, split_folios);
>  
>  					if (!ret) {