From: Andrew Morton <akpm@linux-foundation.org>
To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: mhocko@suse.com, dvyukov@google.com, catalin.marinas@arm.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: page_alloc: document kmemleak's non-blockable __GFP_NOFAIL case
Date: Wed, 24 Jul 2019 19:48:35 -0700 [thread overview]
Message-ID: <20190724194835.59947a6b4df3c2ae7816470d@linux-foundation.org> (raw)
In-Reply-To: <1562964544-59519-1-git-send-email-yang.shi@linux.alibaba.com>
On Sat, 13 Jul 2019 04:49:04 +0800 Yang Shi <yang.shi@linux.alibaba.com> 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:
>
> ...
>
> The mempool_alloc_slab() clears __GFP_DIRECT_RECLAIM, kmemleak has
> __GFP_NOFAIL set all the time due to commit
> d9570ee3bd1d4f20ce63485f5ef05663866fe6c0 ("kmemleak: allow to coexist
> with fault injection").
>
> The fault-injection would not try to fail slab or page allocation if
> __GFP_NOFAIL is used and that commit tries to turn off fault injection
> for kmemleak allocation. Although __GFP_NOFAIL doesn't guarantee no
> failure for all the cases (i.e. non-blockable allocation may fail), it
> still makes sense to the most cases. Kmemleak is also a debugging tool,
> so it sounds not worth changing the behavior.
>
> It also meaks sense to keep the warning, so just document the special
> case in the comment.
>
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4531,8 +4531,14 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
> */
> if (gfp_mask & __GFP_NOFAIL) {
> /*
> - * All existing users of the __GFP_NOFAIL are blockable, so warn
> - * of any new users that actually require GFP_NOWAIT
> + * The users of the __GFP_NOFAIL are expected be blockable,
> + * and this is true for the most cases except for kmemleak.
> + * The kmemleak pass in __GFP_NOFAIL to skip fault injection,
> + * however kmemleak may allocate object at some non-blockable
> + * context to trigger this warning.
> + *
> + * Keep this warning since it is still useful for the most
> + * normal cases.
> */
Comment has rather a lot of typos. I'd normally fix them but I think
I'll duck this patch until the kmemleak situation is addressed, so we
can add a kmemleakless long-term comment, if desired.
next prev parent reply other threads:[~2019-07-25 2:48 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-12 20:49 [PATCH] mm: page_alloc: document kmemleak's non-blockable __GFP_NOFAIL case Yang Shi
2019-07-13 19:39 ` David Rientjes
2019-07-15 3:43 ` Yang Shi
2019-07-15 13:18 ` Michal Hocko
2019-07-13 21:25 ` Matthew Wilcox
2019-07-15 3:47 ` Yang Shi
2019-07-15 13:06 ` Matthew Wilcox
2019-07-15 17:00 ` Yang Shi
2019-07-15 13:17 ` Michal Hocko
2019-07-15 15:01 ` Catalin Marinas
2019-07-15 15:18 ` Qian Cai
2019-07-15 16:58 ` Yang Shi
2019-07-16 17:38 ` Yang Shi
2019-07-25 2:48 ` Andrew Morton [this message]
2019-07-25 17:21 ` Yang Shi
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