linux-kernel - Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in get_pages_per

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Message-ID: <20160511093435.GA13113@swordfish>
Date:	Wed, 11 May 2016 18:34:35 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Ganesh Mahendran <opensource.ganesh@...il.com>,
	Nitin Gupta <ngupta@...are.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in
 get_pages_per_zspage()

On (05/09/16 14:01), Minchan Kim wrote:
[..]
> > no, we need cltd there. but ZS_MAX_PAGES_PER_ZSPAGE also affects
> > ZS_MIN_ALLOC_SIZE, which is used in several places, like
> > get_size_class_index(). that's why ZS_MAX_PAGES_PER_ZSPAGE data
> > type change `improves' zs_malloc().
> 
> Why not if such simple improves zsmalloc? :)
> Please send a patch.
> 
> Thanks a lot, Sergey!

Hello Minchan,

sorry for long reply, I decided to investigate it a bit further.
with this patch, gcc 6.1 -O2 generates "+13" instructions more,
-Os "-25" instructions less. this +13 ins case is a no-no-no.

	-ss