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Re: [Nbd] [PATCH 4/4] mtd: nand: nandsim: convert to memalloc_noreclaim_*()

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

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