Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak_mask
From: Chunyu Hu
Date: Wed Apr 25 2018 - 05:50:52 EST
----- Original Message -----
> From: "Catalin Marinas" <catalin.marinas@xxxxxxx>
> To: "Michal Hocko" <mhocko@xxxxxxxxxx>
> Cc: "Chunyu Hu" <chuhu.ncepu@xxxxxxxxx>, "Dmitry Vyukov" <dvyukov@xxxxxxxxxx>, "Chunyu Hu" <chuhu@xxxxxxxxxx>, "LKML"
> <linux-kernel@xxxxxxxxxxxxxxx>, "Linux-MM" <linux-mm@xxxxxxxxx>
> Sent: Tuesday, April 24, 2018 9:41:48 PM
> Subject: Re: [RFC] mm: kmemleak: replace __GFP_NOFAIL to GFP_NOWAIT in gfp_kmemleak_mask
> On Tue, Apr 24, 2018 at 07:20:57AM -0600, Michal Hocko wrote:
> > On Mon 23-04-18 12:17:32, Chunyu Hu wrote:
> > [...]
> > > So if there is a new flag, it would be the 25th bits.
> > No new flags please. Can you simply store a simple bool into
> > fail_page_alloc
> > and have save/restore api for that?
> For kmemleak, we probably first hit failslab. Something like below may
> do the trick:
> diff --git a/mm/failslab.c b/mm/failslab.c
> index 1f2f248e3601..63f13da5cb47 100644
> --- a/mm/failslab.c
> +++ b/mm/failslab.c
> @@ -29,6 +29,9 @@ bool __should_failslab(struct kmem_cache *s, gfp_t
> if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
> return false;
> + if (s->flags & SLAB_NOLEAKTRACE)
> + return false;
> return should_fail(&failslab.attr, s->object_size);
This maybe is the easy enough way for skipping fault injection for kmemleak slab object.
> Can we get a second should_fail() via should_fail_alloc_page() if a new
> slab page is allocated?
looking at code path blow, what do you mean by getting a second should_fail() via
fail_alloc_page? Seems we need to insert the flag between alloc_slab_page and
alloc_pages()? Without GFP flag, it's difficult to pass info to should_fail_alloc_page
and keep simple at same time.
Or as Michal suggested, completely disabling page alloc fail injection when kmemleak
enabled. And enable it again when kmemleak off.
<========= flag to change the behavior of should_fail_alloc_page