When failslab was originally written, the intention of the
"ignore-gfp-wait" flag default value ("N") was to fail
GFP_ATOMIC allocations. Those were defined as (__GFP_HIGH),
and the code would test for __GFP_WAIT (0x10u).
However, since then, __GFP_WAIT was replaced by __GFP_RECLAIM
(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM), and GFP_ATOMIC is
now defined as (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM).
This means that when the flag is false, almost no allocation
ever fails (as even GFP_ATOMIC allocations contain
__GFP_KSWAPD_RECLAIM).
Restore the original intent of the code, by ignoring calls
that directly reclaim only (___GFP_DIRECT_RECLAIM), and thus,
failing GFP_ATOMIC calls again by default.
Fixes: 71baba4b92dc1fa1 ("mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM")
Signed-off-by: Nicolas Boichat <[email protected]>
---
mm/failslab.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/failslab.c b/mm/failslab.c
index ec5aad211c5be97..33efcb60e633c0a 100644
--- a/mm/failslab.c
+++ b/mm/failslab.c
@@ -23,7 +23,8 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
if (gfpflags & __GFP_NOFAIL)
return false;
- if (failslab.ignore_gfp_reclaim && (gfpflags & __GFP_RECLAIM))
+ if (failslab.ignore_gfp_reclaim &&
+ (gfpflags & ___GFP_DIRECT_RECLAIM))
return false;
if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
--
2.21.0.1020.gf2820cf01a-goog
2019年5月20日(月) 13:49 Nicolas Boichat <[email protected]>:
>
> When failslab was originally written, the intention of the
> "ignore-gfp-wait" flag default value ("N") was to fail
> GFP_ATOMIC allocations. Those were defined as (__GFP_HIGH),
> and the code would test for __GFP_WAIT (0x10u).
>
> However, since then, __GFP_WAIT was replaced by __GFP_RECLAIM
> (___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM), and GFP_ATOMIC is
> now defined as (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM).
>
> This means that when the flag is false, almost no allocation
> ever fails (as even GFP_ATOMIC allocations contain
> __GFP_KSWAPD_RECLAIM).
>
> Restore the original intent of the code, by ignoring calls
> that directly reclaim only (___GFP_DIRECT_RECLAIM), and thus,
> failing GFP_ATOMIC calls again by default.
>
> Fixes: 71baba4b92dc1fa1 ("mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM")
> Signed-off-by: Nicolas Boichat <[email protected]>
Good catch.
Reviewed-by: Akinobu Mita <[email protected]>
> ---
> mm/failslab.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/failslab.c b/mm/failslab.c
> index ec5aad211c5be97..33efcb60e633c0a 100644
> --- a/mm/failslab.c
> +++ b/mm/failslab.c
> @@ -23,7 +23,8 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> if (gfpflags & __GFP_NOFAIL)
> return false;
>
> - if (failslab.ignore_gfp_reclaim && (gfpflags & __GFP_RECLAIM))
> + if (failslab.ignore_gfp_reclaim &&
> + (gfpflags & ___GFP_DIRECT_RECLAIM))
> return false;
Should we use __GFP_DIRECT_RECLAIM instead of ___GFP_DIRECT_RECLAIM?
Because I found the following comment in gfp.h
/* Plain integer GFP bitmasks. Do not use this directly. */
On Tue, 21 May 2019, Akinobu Mita wrote:
> > When failslab was originally written, the intention of the
> > "ignore-gfp-wait" flag default value ("N") was to fail
> > GFP_ATOMIC allocations. Those were defined as (__GFP_HIGH),
> > and the code would test for __GFP_WAIT (0x10u).
> >
> > However, since then, __GFP_WAIT was replaced by __GFP_RECLAIM
> > (___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM), and GFP_ATOMIC is
> > now defined as (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM).
> >
> > This means that when the flag is false, almost no allocation
> > ever fails (as even GFP_ATOMIC allocations contain
> > __GFP_KSWAPD_RECLAIM).
> >
> > Restore the original intent of the code, by ignoring calls
> > that directly reclaim only (___GFP_DIRECT_RECLAIM), and thus,
> > failing GFP_ATOMIC calls again by default.
> >
> > Fixes: 71baba4b92dc1fa1 ("mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM")
> > Signed-off-by: Nicolas Boichat <[email protected]>
>
> Good catch.
>
> Reviewed-by: Akinobu Mita <[email protected]>
>
> > ---
> > mm/failslab.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/failslab.c b/mm/failslab.c
> > index ec5aad211c5be97..33efcb60e633c0a 100644
> > --- a/mm/failslab.c
> > +++ b/mm/failslab.c
> > @@ -23,7 +23,8 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> > if (gfpflags & __GFP_NOFAIL)
> > return false;
> >
> > - if (failslab.ignore_gfp_reclaim && (gfpflags & __GFP_RECLAIM))
> > + if (failslab.ignore_gfp_reclaim &&
> > + (gfpflags & ___GFP_DIRECT_RECLAIM))
> > return false;
>
> Should we use __GFP_DIRECT_RECLAIM instead of ___GFP_DIRECT_RECLAIM?
> Because I found the following comment in gfp.h
>
> /* Plain integer GFP bitmasks. Do not use this directly. */
>
Yes, we should use the two underscore version instead of the three.
Nicolas, after that's fixed up, feel free to add Acked-by: David Rientjes
<[email protected]>.
Thanks!
On Tue, May 21, 2019 at 12:29 AM Akinobu Mita <[email protected]> wrote:
>
> 2019年5月20日(月) 13:49 Nicolas Boichat <[email protected]>:
> >
> > When failslab was originally written, the intention of the
> > "ignore-gfp-wait" flag default value ("N") was to fail
> > GFP_ATOMIC allocations. Those were defined as (__GFP_HIGH),
> > and the code would test for __GFP_WAIT (0x10u).
> >
> > However, since then, __GFP_WAIT was replaced by __GFP_RECLAIM
> > (___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM), and GFP_ATOMIC is
> > now defined as (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM).
> >
> > This means that when the flag is false, almost no allocation
> > ever fails (as even GFP_ATOMIC allocations contain
> > __GFP_KSWAPD_RECLAIM).
> >
> > Restore the original intent of the code, by ignoring calls
> > that directly reclaim only (___GFP_DIRECT_RECLAIM), and thus,
> > failing GFP_ATOMIC calls again by default.
> >
> > Fixes: 71baba4b92dc1fa1 ("mm, page_alloc: rename __GFP_WAIT to __GFP_RECLAIM")
> > Signed-off-by: Nicolas Boichat <[email protected]>
>
> Good catch.
>
> Reviewed-by: Akinobu Mita <[email protected]>
>
> > ---
> > mm/failslab.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/failslab.c b/mm/failslab.c
> > index ec5aad211c5be97..33efcb60e633c0a 100644
> > --- a/mm/failslab.c
> > +++ b/mm/failslab.c
> > @@ -23,7 +23,8 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> > if (gfpflags & __GFP_NOFAIL)
> > return false;
> >
> > - if (failslab.ignore_gfp_reclaim && (gfpflags & __GFP_RECLAIM))
> > + if (failslab.ignore_gfp_reclaim &&
> > + (gfpflags & ___GFP_DIRECT_RECLAIM))
> > return false;
>
> Should we use __GFP_DIRECT_RECLAIM instead of ___GFP_DIRECT_RECLAIM?
> Because I found the following comment in gfp.h
>
> /* Plain integer GFP bitmasks. Do not use this directly. */
Oh, nice catch. I must say I had no idea I was using the 3-underscore
version, hard to tell them apart depending on the font.
I'll send a v2 with both your tags right away.
Thanks,
Hi Nicolas,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v5.2-rc1 next-20190520]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Nicolas-Boichat/mm-failslab-By-default-do-not-fail-allocations-with-direct-reclaim-only/20190521-045221
reproduce:
# apt-get install sparse
make ARCH=x86_64 allmodconfig
make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <[email protected]>
sparse warnings: (new ones prefixed by >>)
>> mm/failslab.c:27:26: sparse: sparse: restricted gfp_t degrades to integer
vim +27 mm/failslab.c
16
17 bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
18 {
19 /* No fault-injection for bootstrap cache */
20 if (unlikely(s == kmem_cache))
21 return false;
22
23 if (gfpflags & __GFP_NOFAIL)
24 return false;
25
26 if (failslab.ignore_gfp_reclaim &&
> 27 (gfpflags & ___GFP_DIRECT_RECLAIM))
28 return false;
29
30 if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
31 return false;
32
33 return should_fail(&failslab.attr, s->object_size);
34 }
35
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
On Tue, May 21, 2019 at 4:01 PM kbuild test robot <[email protected]> wrote:
> sparse warnings: (new ones prefixed by >>)
>
> >> mm/failslab.c:27:26: sparse: sparse: restricted gfp_t degrades to integer
> 26 if (failslab.ignore_gfp_reclaim &&
> > 27 (gfpflags & ___GFP_DIRECT_RECLAIM))
That was for v1, fixed in v2 already.