linux-kernel - Re: [PATCH 1/4] mm/zsmalloc: always set movable/highmem flag to the zspage

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Message-ID: <20170321111005.GA28016@bbox>
Date:   Tue, 21 Mar 2017 20:10:05 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     <js1304@...il.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        <linux-kernel@...r.kernel.org>, <kernel-team@....com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 1/4] mm/zsmalloc: always set movable/highmem flag to the
 zspage

Hi Joonsoo,

On Thu, Mar 16, 2017 at 11:46:35AM +0900, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> Zspage is always movable and is used through zs_map_object() function
> which returns directly accessible pointer that contains content of
> zspage. It is independent on the user's allocation flag.
> Therefore, it's better to always set movable/highmem flag to the zspage.
> After that, we don't need __GFP_MOVABLE/__GFP_HIGHMEM clearing in
> cache_alloc_handle()/cache_alloc_zspage() since there is no zs_malloc
> caller who specifies __GFP_MOVABLE/__GFP_HIGHMEM.

Hmm, I wanted this when you pointed out to me firstly but when I think
again, I don't see it's improvement. Sorry for that.
The zs_malloc is exported symbol and it has gfp_t argument so user can
do whatever he want with any zone modifiers flags. IOW, if someuser want
to allocate pages from {normal|dma} zone by whatever reason, he can
omit __GFP_HIGHMEM from the gfp flag to fullfill the goal.