linux-kernel - Re: [RFC 2/7] mm/vmalloc: Support non-blocking GFP flags in alloc_vmap

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Message-ID: <aG1LPktW1l3IKjEb@pc636>
Date: Tue, 8 Jul 2025 18:45:50 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>
Subject: Re: [RFC 2/7] mm/vmalloc: Support non-blocking GFP flags in
 alloc_vmap_area()

On Tue, Jul 08, 2025 at 05:17:33PM +0200, Michal Hocko wrote:
> On Tue 08-07-25 14:34:28, Uladzislau Rezki wrote:
> > On Mon, Jul 07, 2025 at 09:11:35AM +0200, Michal Hocko wrote:
> > > On Fri 04-07-25 17:25:32, Uladzislau Rezki wrote:
> > > [...]
> > > > @@ -2030,7 +2033,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
> > > >  	 */
> > > >  	va = node_alloc(size, align, vstart, vend, &addr, &vn_id);
> > > >  	if (!va) {
> > > > -		gfp_mask = gfp_mask & GFP_RECLAIM_MASK;
> > > > +		if (allow_block)
> > > > +			gfp_mask = gfp_mask & GFP_RECLAIM_MASK;
> > > 
> > > I don't follow here and is this even correct?
> > > 
> > Allow nested flags to follow a user request if there is a request
> > to not block. For example if we apply GFP_RECLAIM_MASK to GFP_ATOMIC
> > GFP_ATOMIC is converted to zero, thus to GFP_NOWAIT.
> 
> I still do not follow. The aim of this code is to filter out all
> non-reclaim related flags. Why that should work differently for
> non-waiting allocations?
> Btw. if you had GPP_ATOMIC the resulting mask will be still GFP_ATOMIC
> as both __GFP_HIGH|__GFP_KSWAPD_RECLAIM are part of GFP_RECLAIM_MASK.
> 
Right. I misread the GFP_RECLAIM_MASK, i thought that GFP_ATOMIC and
GFP_NOWAIT are not part of it. They allow reclaim, but not direct,
i.e. it is OK to wake-up a kswapd.

So, they should not work differently. Thank you for the comment! 

--
Uladzislau Rezki