linux-kernel - Re: [PATCH v4] kmemleak: survive in a low-memory situation

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Message-ID: <20190327182158.GS10344@bombadil.infradead.org>
Date:   Wed, 27 Mar 2019 11:21:58 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Michal Hocko <mhocko@...nel.org>, Qian Cai <cai@....pw>,
        akpm@...ux-foundation.org, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation

On Wed, Mar 27, 2019 at 05:29:57PM +0000, Catalin Marinas wrote:
> On Wed, Mar 27, 2019 at 09:44:32AM +0100, Michal Hocko wrote:
> > As long as there is an implicit __GFP_NOFAIL then kmemleak is simply
> > broken no matter what other gfp flags you play with. Has anybody looked
> > at some sort of preallocation where gfpflags_allow_blocking context
> > allocate objects into a pool that non-sleeping allocations can eat from?
> 
> Quick attempt below and it needs some more testing (pretty random pick
> of the EMERGENCY_POOL_SIZE value). Also, with __GFP_NOFAIL removed, are
> the other flags safe or we should trim them further?

Why not use mempool?

>  #define gfp_kmemleak_mask(gfp)	(((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \
>  				 __GFP_NORETRY | __GFP_NOMEMALLOC | \
> -				 __GFP_NOWARN | __GFP_NOFAIL)
> +				 __GFP_NOWARN)

Why GFP_NORETRY?  And if I have specified one of the other retry policies
in my gfp flags, you should presumably clear that off before setting
GFP_NORETRY.