Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
From:   "NeilBrown" <neilb@suse.de>
To:     "Matthew Wilcox" <willy@infradead.org>
Cc:     "Andrew Morton" <akpm@linux-foundation.org>,
        "Michal Hocko" <mhocko@suse.com>,
        "Thierry Reding" <thierry.reding@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] MM: discard __GFP_ATOMIC
In-reply-to: <YZUBIbALcSHn4Rub@casper.infradead.org>
References: <163712397076.13692.4727608274002939094@noble.neil.brown.name>,
 <YZUBIbALcSHn4Rub@casper.infradead.org>
Date:   Fri, 19 Nov 2021 10:14:38 +1100
Message-id: <163727727803.13692.15470049610672496362@noble.neil.brown.name>
Precedence: bulk

On Thu, 18 Nov 2021, Matthew Wilcox wrote:
> On Wed, Nov 17, 2021 at 03:39:30PM +1100, NeilBrown wrote:
> > +++ b/drivers/iommu/tegra-smmu.c
> > @@ -676,12 +676,12 @@ static struct page *as_get_pde_page(struct tegra_sm=
mu_as *as,
> >  	 * allocate page in a sleeping context if GFP flags permit. Hence
> >  	 * spinlock needs to be unlocked and re-locked after allocation.
> >  	 */
> > -	if (!(gfp & __GFP_ATOMIC))
> > +	if (gfp & __GFP_DIRECT_RECLAIM)
> >  		spin_unlock_irqrestore(&as->lock, *flags);
> > =20
> >  	page =3D alloc_page(gfp | __GFP_DMA | __GFP_ZERO);
> > =20
> > -	if (!(gfp & __GFP_ATOMIC))
> > +	if (gfp & __GFP_DIRECT_RECLAIM)
> >  		spin_lock_irqsave(&as->lock, *flags);
> > =20
> >  	/*
>=20
> Surely this should be gfpflags_allow_blocking() instead of poking about
> in the innards of gfp flags?

Possibly.  Didn't know about gfpflags_allow_blocking().  From a quick
grep in the kernel, a whole lot of other people don't know about it
either, though clearly some do.

Maybe we should reaname "__GFP_DIRECT_RECLAIM" to
"__GFP_ALLOW_BLOCKING", because that is what most users seems to care
about.

If not, then we probably want a gfpflags_without_block() function that
removes that flag, as lots of code wants to do that - and using the flag
for one, and an inline for the other is not consistent.

My leaning would be to __GFP_ALLOW_BLOCKING

NeilBrown


>=20
> This patch seems like a good simplification to me.
>=20
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Thanks,
NeilBrown