linux-kernel - Re: [PATCH v2] mm/page-writeback.c: write_cache

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Message-ID: <20200219002004.GC14509@iweiny-DESK2.sc.intel.com>
Date:   Tue, 18 Feb 2020 16:20:05 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Mauricio Faria de Oliveira <mfo@...onical.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/page-writeback.c: write_cache_pages(): deduplicate
 identical checks

On Tue, Feb 18, 2020 at 07:17:16PM -0300, Mauricio Faria de Oliveira wrote:
> There used to be a 'retry' label in between the two (identical) checks
> when first introduced in commit f446daaea9d4 ("mm: implement writeback
> livelock avoidance using page tagging"), and later modified/updated in
> commit 6e6938b6d313 ("writeback: introduce .tagged_writepages for the
> WB_SYNC_NONE sync stage").
> 
> The label has been removed in commit 64081362e8ff ("mm/page-writeback.c:
> fix range_cyclic writeback vs writepages deadlock"), and the (identical)
> checks are now present / performed immediately one after another.
> 
> So, remove/deduplicate the latter check, moving tag_pages_for_writeback()
> into the former check before the 'tag' variable assignment, so it's clear
> that it's not used in this (similarly-named) function call but only later
> in pagevec_lookup_range_tag().
> 
> Signed-off-by: Mauricio Faria de Oliveira <mfo@...onical.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> ---
> 
>  v2: add the missing braces to the conditional statement
>      with more than a single statement.. doh; and to the
>      else branch (w/a single statement, per coding style.)
> 
>  mm/page-writeback.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2caf780a42e7..ab5a3cee8ad3 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2182,12 +2182,12 @@ int write_cache_pages(struct address_space *mapping,
>  		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
>  			range_whole = 1;
>  	}
> -	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
> +	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
> +		tag_pages_for_writeback(mapping, index, end);
>  		tag = PAGECACHE_TAG_TOWRITE;
> -	else
> +	} else {
>  		tag = PAGECACHE_TAG_DIRTY;
> -	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
> -		tag_pages_for_writeback(mapping, index, end);
> +	}
>  	done_index = index;
>  	while (!done && (index <= end)) {
>  		int i;
> -- 
> 2.20.1
>