linux-kernel - Re: [PATCH] mm: page_alloc: document kmemleak's non-blockable __GFP

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Message-ID: <20190715130648.GA32320@bombadil.infradead.org>
Date:   Mon, 15 Jul 2019 06:06:48 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     mhocko@...e.com, dvyukov@...gle.com, catalin.marinas@....com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: document kmemleak's non-blockable
 __GFP_NOFAIL case

On Sun, Jul 14, 2019 at 08:47:07PM -0700, Yang Shi wrote:
> 
> 
> On 7/13/19 2:25 PM, Matthew Wilcox wrote:
> > On Sat, Jul 13, 2019 at 04:49:04AM +0800, Yang Shi wrote:
> > > When running ltp's oom test with kmemleak enabled, the below warning was
> > > triggerred since kernel detects __GFP_NOFAIL & ~__GFP_DIRECT_RECLAIM is
> > > passed in:
> > There are lots of places where kmemleak will call kmalloc with
> > __GFP_NOFAIL and ~__GFP_DIRECT_RECLAIM (including the XArray code, which
> > is how I know about it).  It needs to be fixed to allow its internal
> > allocations to fail and return failure of the original allocation as
> > a consequence.
> 
> Do you mean kmemleak internal allocation? It would fail even though
> __GFP_NOFAIL is passed in if GFP_NOWAIT is specified. Currently buddy
> allocator will not retry if the allocation is non-blockable.

Actually it sets off a warning.  Which is the right response from the
core mm code because specifying __GFP_NOFAIL and __GFP_NOWAIT makes no
sense.