linux-kernel - Re: [PATCH 17/19] dm: get rid of superfluous gfp flags

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Message-ID: <20160416203135.GC15128@dhcp22.suse.cz>
Date:	Sat, 16 Apr 2016 16:31:36 -0400
From:	Michal Hocko <mhocko@...nel.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Shaohua Li <shli@...nel.org>
Subject: Re: [PATCH 17/19] dm: get rid of superfluous gfp flags

On Fri 15-04-16 14:41:29, Mikulas Patocka wrote:
> 
> 
> On Fri, 15 Apr 2016, Michal Hocko wrote:
> 
> > On Fri 15-04-16 08:29:28, Mikulas Patocka wrote:
> > > 
> > > 
> > > On Mon, 11 Apr 2016, Michal Hocko wrote:
> > > 
> > > > From: Michal Hocko <mhocko@...e.com>
> > > > 
> > > > copy_params seems to be little bit confused about which allocation flags
> > > > to use. It enforces GFP_NOIO even though it uses
> > > > memalloc_noio_{save,restore} which enforces GFP_NOIO at the page
> > > 
> > > memalloc_noio_{save,restore} is used because __vmalloc is flawed and 
> > > doesn't respect GFP_NOIO properly (it doesn't use gfp flags when 
> > > allocating pagetables).
> > 
> > Yes and there are no plans to change __vmalloc to properly propagate gfp
> > flags through the whole call chain and that is why we have
> > memalloc_noio thingy. If that ever changes later the GFP_NOIO can be
> > added in favor of memalloc_noio API. Both are clearly redundant.
> > -- 
> > Michal Hocko
> > SUSE Labs
> 
> You could move memalloc_noio_{save,restore} to __vmalloc. Something like
> 
> if (!(gfp_mask & __GFP_IO))
> 	noio_flag = memalloc_noio_save();
> ...
> if (!(gfp_mask & __GFP_IO))
> 	memalloc_noio_restore(noio_flag);
> 
> That would be better than repeating this hack in every __vmalloc caller 
> that need GFP_NOIO.

It is not my intention to change __vmalloc behavior. If you strongly
oppose the GFP_NOIO change I can drop it from the patch. It is
__GFP_REPEAT which I am after.

-- 
Michal Hocko
SUSE Labs