linux-kernel - Re: [PATCH v1 4/6] memcg-v1: no need for memcg locking for writeback tracking

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Message-ID: <ZxtBW9d4bkj9C7gY@tiehlicka>
Date: Fri, 25 Oct 2024 08:57:31 +0200
From: Michal Hocko <mhocko@...e.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Hugh Dickins <hughd@...gle.com>,
	Yosry Ahmed <yosryahmed@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH v1 4/6] memcg-v1: no need for memcg locking for writeback
 tracking

On Thu 24-10-24 18:23:01, Shakeel Butt wrote:
> During the era of memcg charge migration, the kernel has to be make sure
> that the writeback stat updates do not race with the charge migration.
> Otherwise it might update the writeback stats of the wrong memcg. Now
> with the memcg charge migration deprecated, there is no more race for

s@...recated@...e

> writeback stat updates and the previous locking can be removed.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>

Acked-by: Michal Hocko <mhocko@...e.com>
Thanks!

> ---
>  mm/page-writeback.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index a76a73529fd9..9c3317c3a615 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -3083,7 +3083,6 @@ bool __folio_end_writeback(struct folio *folio)
>  	struct address_space *mapping = folio_mapping(folio);
>  	bool ret;
>  
> -	folio_memcg_lock(folio);
>  	if (mapping && mapping_use_writeback_tags(mapping)) {
>  		struct inode *inode = mapping->host;
>  		struct backing_dev_info *bdi = inode_to_bdi(inode);
> @@ -3114,7 +3113,6 @@ bool __folio_end_writeback(struct folio *folio)
>  	lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
>  	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
>  	node_stat_mod_folio(folio, NR_WRITTEN, nr);
> -	folio_memcg_unlock(folio);
>  
>  	return ret;
>  }
> @@ -3127,7 +3125,6 @@ void __folio_start_writeback(struct folio *folio, bool keep_write)
>  
>  	VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
>  
> -	folio_memcg_lock(folio);
>  	if (mapping && mapping_use_writeback_tags(mapping)) {
>  		XA_STATE(xas, &mapping->i_pages, folio_index(folio));
>  		struct inode *inode = mapping->host;
> @@ -3168,7 +3165,6 @@ void __folio_start_writeback(struct folio *folio, bool keep_write)
>  
>  	lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
>  	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
> -	folio_memcg_unlock(folio);
>  
>  	access_ret = arch_make_folio_accessible(folio);
>  	/*
> -- 
> 2.43.5

-- 
Michal Hocko
SUSE Labs