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

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Message-ID: <fe1c21a4-0bc6-529c-5446-382b01d4c99e@intel.com>
Date:   Thu, 6 Apr 2017 09:33:44 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        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>
Subject: Re: [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*()

On 05/04/17 14:39, Vlastimil Babka wrote:
> 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.

IIRC it was to avoid getting stuck with nandsim waiting on memory reclaim
and memory reclaim waiting on nandsim.