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Date: Wed, 11 May 2016 18:34:35 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in
 get_pages_per_zspage()
Message-ID: <20160511093435.GA13113@swordfish>
References: <1462425447-13385-1-git-send-email-opensource.ganesh@gmail.com>
 <20160505100329.GA497@swordfish>
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 <CADAEsF9S4GQE6V+zsvRRVYjdbfN3VRQFcTiN5E_MWw60bfk0Zw@mail.gmail.com>
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Sender: owner-linux-mm@kvack.org
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To: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Ganesh Mahendran <opensource.ganesh@gmail.com>, Nitin Gupta <ngupta@vflare.org>, Andrew Morton <akpm@linux-foundation.org>, Linux-MM <linux-mm@kvack.org>, linux-kernel <linux-kernel@vger.kernel.org>

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

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