linux-kernel - Re: [PATCH v2 0/4] extend vmalloc support for constrained allocations

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Message-ID: <20211125213034.GQ418105@dread.disaster.area>
Date:   Fri, 26 Nov 2021 08:30:34 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@....de>,
        Uladzislau Rezki <urezki@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v2 0/4] extend vmalloc support for constrained allocations

On Thu, Nov 25, 2021 at 10:30:28AM +0100, Michal Hocko wrote:
> [Cc Sebastian and Vlastimil]
> 
> On Thu 25-11-21 09:58:31, Michal Hocko wrote:
> > On Thu 25-11-21 09:55:26, Dave Chinner wrote:
> > [...]
> > > Correct __GFP_NOLOCKDEP support is also needed. See:
> > > 
> > > https://lore.kernel.org/linux-mm/20211119225435.GZ449541@dread.disaster.area/
> > 
> > I will have a closer look. This will require changes on both vmalloc and
> > sl?b sides.
> 
> This should hopefully make the trick
> --- 
> From 0082d29c771d831e5d1b9bb4c0a61d39bac017f0 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Thu, 25 Nov 2021 10:20:16 +0100
> Subject: [PATCH] mm: make slab and vmalloc allocators __GFP_NOLOCKDEP aware
> 
> sl?b and vmalloc allocators reduce the given gfp mask for their internal
> needs. For that they use GFP_RECLAIM_MASK to preserve the reclaim
> behavior and constrains.
> 
> __GFP_NOLOCKDEP is not a part of that mask because it doesn't really
> control the reclaim behavior strictly speaking. On the other hand
> it tells the underlying page allocator to disable reclaim recursion
> detection so arguably it should be part of the mask.
> 
> Having __GFP_NOLOCKDEP in the mask will not alter the behavior in any
> form so this change is safe pretty much by definition. It also adds
> a support for this flag to SL?B and vmalloc allocators which will in
> turn allow its use to kvmalloc as well. A lack of the support has been
> noticed recently in http://lkml.kernel.org/r/20211119225435.GZ449541@dread.disaster.area
> 
> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/internal.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index 3b79a5c9427a..2ceea20b5b2a 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -21,7 +21,7 @@
>  #define GFP_RECLAIM_MASK (__GFP_RECLAIM|__GFP_HIGH|__GFP_IO|__GFP_FS|\
>  			__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NOFAIL|\
>  			__GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC|\
> -			__GFP_ATOMIC)
> +			__GFP_ATOMIC|__GFP_NOLOCKDEP)
>  
>  /* The GFP flags allowed during early boot */
>  #define GFP_BOOT_MASK (__GFP_BITS_MASK & ~(__GFP_RECLAIM|__GFP_IO|__GFP_FS))

Looks reasonable to me.

Acked-by: Dave Chinner <dchinner@...hat.com>

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com