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

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Message-ID: <a991ac12-3610-f993-e44c-b12adab17fe1@linux.alibaba.com>
Date:   Mon, 15 Jul 2019 10:00:34 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Matthew Wilcox <willy@...radead.org>
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 7/15/19 6:06 AM, Matthew Wilcox wrote:
> 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.

Yes, this is what I meant. Kmemleak did a trick to fool fault-injection 
by passing in __GFP_NOFAIL, but it doesn't make sense for non-blockable 
allocation.