netdev - Re: [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim

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Message-ID: <9b9d5bca-e125-e07b-b700-196cc800bbd7@suse.cz>
Date:   Wed, 5 Apr 2017 13:39:16 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Richard Weinberger <richard@....at>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-block@...r.kernel.org, nbd-general@...ts.sourceforge.net,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org,
        netdev@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*()

On 04/05/2017 01:36 PM, Richard Weinberger wrote:
> Michal,
> 
> Am 05.04.2017 um 13:31 schrieb Michal Hocko:
>> On Wed 05-04-17 09:47:00, Vlastimil Babka wrote:
>>> Nandsim has own functions set_memalloc() and clear_memalloc() for robust
>>> setting and clearing of PF_MEMALLOC. Replace them by the new generic helpers.
>>> No functional change.
>>
>> This one smells like an abuser. Why the hell should read/write path
>> touch memory reserves at all!
> 
> Could be. Let's ask Adrian, AFAIK he wrote that code.
> Adrian, can you please clarify why nandsim needs to play with PF_MEMALLOC?

I was thinking about it and concluded that since the simulator can be
used as a block device where reclaimed pages go to, writing the data out
is a memalloc operation. Then reading can be called as part of r-m-w
cycle, so reading as well. But it would be great if somebody more
knowledgeable confirmed this.

> Thanks,
> //richard
>