Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <628c9cb4.1c69fb81.aec05.30a1@mx.google.com>
Date:   Tue, 24 May 2022 08:52:02 +0000
From:   CGEL <cgel.zte@gmail.com>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Balbir Singh <bsingharora@gmail.com>, akpm@linux-foundation.org,
        ammarfaizi2@gnuweeb.org, oleksandr@natalenko.name,
        willy@infradead.org, linux-mm@kvack.org, corbet@lwn.net,
        linux-kernel@vger.kernel.org, xu xin <xu.xin16@zte.com.cn>,
        Yang Yang <yang.yang29@zte.com.cn>,
        Ran Xiaokai <ran.xiaokai@zte.com.cn>,
        wangyong <wang.yong12@zte.com.cn>,
        Yunkai Zhang <zhang.yunkai@zte.com.cn>,
        Jiang Xuexin <jiang.xuexin@zte.com.cn>
Subject: Re: [PATCH] mm/ksm: introduce ksm_enabled for each processg
References: <20220517092701.1662641-1-xu.xin16@zte.com.cn>
 <YoSZE7Iak3AYA4VE@balbir-desktop>
 <6284a2ef.1c69fb81.e53cd.32b2@mx.google.com>
 <YoTjJH7+QD+DSrW8@dhcp22.suse.cz>
 <6285e519.1c69fb81.4f3fe.8057@mx.google.com>
 <YoX0TWoNw3HqH/X/@dhcp22.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YoX0TWoNw3HqH/X/@dhcp22.suse.cz>
Precedence: bulk

On Thu, May 19, 2022 at 09:39:57AM +0200, Michal Hocko wrote:
> On Thu 19-05-22 06:35:03, CGEL wrote:
> > On Wed, May 18, 2022 at 02:14:28PM +0200, Michal Hocko wrote:
> > > On Wed 18-05-22 07:40:30, CGEL wrote:
> > > [...]
> > > > 2. process_madvise is still a kind of madvise. processs_madvise from
> > > > another process overrides the intention of origin app code ifself that
> > > > also calls madvise, which is unrecoverable. For example, if a process "A"
> > > > which madvises just one part of VMAs (not all) as MERGEABLE run on the OS
> > > > already, meanwhile, if another process which doesn't know the information
> > > > of "A" 's MERGEABLE areas, then call process_madvise to advise all VMAs of
> > > > "A" as MERGEABLE, the original MERGEABLE information of "A" calling madivse
> > > > is erasured permanently.
> > > 
> > > I do not really follow. How is this any different from an external
> > > process modifying the process wide policy via the proc or any other
> > > interface?
> > 
> > In this patch, you can see that we didn't modify the flag of any VMA of
> > the target process, which is different from process_madvise. So it is
> > easy to keep the original MERGEABLE information of the target process
> > when we turn back to the default state from the state "always".
> 
> This means that /proc/<pid>/smaps doesn't show the real state, right?

Maybe we can add extra information of KSM forcible state in /proc/<pid>/smaps
like THPeligible. 

Really, Michal, I think it again, 'process_ madvise' is really not good. In
addition to some shortcomings I said before, If new vmas of the target process
are created after the external process calls process_madvise(), then we have to
call `process_madvise()` on them again, over and over again, regularly, just like
Oleksandr said [1].

[1]: https://lore.kernel.org/lkml/1817008.tdWV9SEqCh@natalenko.name/


> 
> -- 
> Michal Hocko
> SUSE Labs