linux-kernel - Re: [PATCH 6/6] mm: Add memalloc

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Message-ID: <20200629125231.GJ32461@dhcp22.suse.cz>
Date:   Mon, 29 Jun 2020 14:52:31 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-xfs@...r.kernel.org, dm-devel@...hat.com,
        Mikulas Patocka <mpatocka@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, NeilBrown <neilb@...e.de>
Subject: Re: [PATCH 6/6] mm: Add memalloc_nowait

On Mon 29-06-20 13:18:16, Matthew Wilcox wrote:
> On Mon, Jun 29, 2020 at 08:08:51AM +0300, Mike Rapoport wrote:
> > > @@ -886,8 +868,12 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
> > >  			return NULL;
> > >  
> > >  		if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
> > > +			unsigned noio_flag;
> > > +
> > >  			dm_bufio_unlock(c);
> > > -			b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
> > > +			noio_flag = memalloc_noio_save();
> > 
> > I've read the series twice and I'm still missing the definition of
> > memalloc_noio_save().
> > 
> > And also it would be nice to have a paragraph about it in
> > Documentation/core-api/memory-allocation.rst
> 
> Documentation/core-api/gfp_mask-from-fs-io.rst:``memalloc_nofs_save``, ``memalloc_nofs_restore`` respectively ``memalloc_noio_save``,
> Documentation/core-api/gfp_mask-from-fs-io.rst:   :functions: memalloc_noio_save memalloc_noio_restore
> Documentation/core-api/gfp_mask-from-fs-io.rst:allows nesting so it is safe to call ``memalloc_noio_save`` or
 
The patch is adding memalloc_nowait* and I suspect Mike had that in
mind, which would be a fair request. Btw. we are missing memalloc_nocma*
documentation either - I was just reminded of its existence today...

-- 
Michal Hocko
SUSE Labs