Re: [Nbd] [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*()
- To: Vlastimil Babka <vbabka@...1290...>
- Cc: nbd-general@lists.sourceforge.net, Boris Brezillon <boris.brezillon@...1551...>, linux-scsi@...25..., Richard Weinberger <richard@...2889...>, linux-kernel@...25..., Adrian Hunter <adrian.hunter@...1303...>, linux-block@...25..., linux-mm@...1312..., netdev@...25..., Johannes Weiner <hannes@...1554...>, Andrew Morton <akpm@...133...>, open-iscsi@...2887..., Mel Gorman <mgorman@...2888...>
- Subject: Re: [Nbd] [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*()
- From: Michal Hocko <mhocko@...1285...>
- Date: Wed, 5 Apr 2017 14:09:36 +0200
- Message-id: <20170405120936.GN6035@...2894...>
- In-reply-to: <9b9d5bca-e125-e07b-b700-196cc800bbd7@...1290...>
- References: <20170405074700.29871-1-vbabka@...1290...> <20170405074700.29871-5-vbabka@...1290...> <20170405113157.GM6035@...2894...> <ee6649ed-b0e8-1c59-c193-d1688fdfe7f5@...2889...> <9b9d5bca-e125-e07b-b700-196cc800bbd7@...1290...>
On Wed 05-04-17 13:39:16, 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. But it would be great if somebody more
> knowledgeable confirmed this.
then this deserves a big fat comment explaining all the details,
including how the complete depletion of reserves is prevented.
--
Michal Hocko
SUSE Labs
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