linux-kernel - Re: [PATCH] swap: Delete the "last_in_cluster < scan_base" loop in the body of scan_swap

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Date:	Mon, 2 Jun 2014 16:26:13 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Chen Yucong <slaoub@...il.com>
cc:	shli@...nel.org, hughd@...gle.com, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] swap: Delete  the "last_in_cluster < scan_base" loop in
 the body of scan_swap_map()

On Mon, 2 Jun 2014, Chen Yucong wrote:

> From commit ebc2a1a69111, we can find that all SWP_SOLIDSTATE "seek is cheap"(SSD case) 
> has already gone to si->cluster_info scan_swap_map_try_ssd_cluster() route. So that the
> "last_in_cluster < scan_base" loop in the body of scan_swap_map() has already become a 
> dead code snippet, and it should have been deleted.
> 
> This patch is to delete the redundant loop as Hugh and Shaohua suggested.
> 
> Signed-off-by: Chen Yucong <slaoub@...il.com>

That is very nice, thank you.

Acked-by: Hugh Dickins <hughd@...gle.com>

But it does beg for just a little more: perhaps Andrew can kindly fold in:
---

 mm/swapfile.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- chen/mm/swapfile.c	2014-06-02 15:55:44.812368186 -0700
+++ hugh/mm/swapfile.c	2014-06-02 16:15:20.344396124 -0700
@@ -505,13 +505,10 @@ static unsigned long scan_swap_map(struc
 		/*
 		 * If seek is expensive, start searching for new cluster from
 		 * start of partition, to minimize the span of allocated swap.
-		 * But if seek is cheap, search from our current position, so
-		 * that swap is allocated from all over the partition: if the
-		 * Flash Translation Layer only remaps within limited zones,
-		 * we don't want to wear out the first zone too quickly.
+		 * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
+		 * case, just handled by scan_swap_map_try_ssd_cluster() above.
 		 */
-		if (!(si->flags & SWP_SOLIDSTATE))
-			scan_base = offset = si->lowest_bit;
+		scan_base = offset = si->lowest_bit;
 		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 
 		/* Locate the first empty (unaligned) cluster */
--
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