Re: [PATCH 8/8] mm: Drop __GFP_DIRECT_RECLAIM flag if PF_MEMALLOC is set

[Uladzislau Rezki <urezki@gmail.com>]

On Fri, Aug 08, 2025 at 04:16:04PM +0200, Michal Hocko wrote:
> On Fri 08-08-25 15:12:45, Uladzislau Rezki wrote:
> > On Thu, Aug 07, 2025 at 01:58:20PM +0200, Michal Hocko wrote:
> > > On Thu 07-08-25 09:58:10, Uladzislau Rezki wrote:
> > > > The memory allocator already avoids reclaim when PF_MEMALLOC is set.
> > > > Clear __GFP_DIRECT_RECLAIM explicitly to suppress might_alloc() warnings
> > > > to make more correct behavior.
> > > 
> > > Rather than chaning the gfp mask would it make more sense to update
> > > might_alloc instead?
> > > 
> > Hm.. I was thinking about it but decided to drop the __GFP_DIRECT_RECLAIM
> > instead just to guarantee a no-reclaim behaviour, as it is written now to
> > the flag.
> > 
> > >From the other hand after this patch we would have some unneeded/dead
> > checks(if i do not missing anything). For example:
> > 
> > [1]
> >     WARN_ON_ONCE(!can_direct_reclaim);
> >     /*
> >      * PF_MEMALLOC request from this context is rather bizarre
> >      * because we cannot reclaim anything and only can loop waiting
> >      * for somebody to do a work for us.
> >      */
> >     WARN_ON_ONCE(current->flags & PF_MEMALLOC);
> > [2]
> >     /* no reclaim without waiting on it */
> >     if (!(gfp_mask & __GFP_DIRECT_RECLAIM))
> >         return false;
> > 
> >     /* this guy won't enter reclaim */
> >     if (current->flags & PF_MEMALLOC)
> >         return false;
> > 
> > [3]
> >     /* Caller is not willing to reclaim, we can't balance anything */
> >     if (!can_direct_reclaim)
> >         goto nopage;
> > 
> >     /* Avoid recursion of direct reclaim */
> >     if (current->flags & PF_MEMALLOC)
> >         goto nopage;
> > etc.
> > 
> > But, yes, might_alloc() can be modified also.
> 
> I do not have a _strong_ preference but my slight preference would be to
> deal with this in might_alloc. Not sure what other think.
> 
No problem, that i can easily switch to.

--
Uladzisau Rezki