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Groups > linux.kernel > #1594437 > unrolled thread

[RFC PATCH 0/4 v2] mm: give __GFP_REPEAT a better semantic

Started byMichal Hocko <mhocko@kernel.org>
First post2017-03-07 18:00 +0100
Last post2017-03-09 09:30 +0100
Articles 5 — 2 participants

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  [RFC PATCH 0/4 v2] mm: give __GFP_REPEAT a better semantic Michal Hocko <mhocko@kernel.org> - 2017-03-07 18:00 +0100
    [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2017-03-07 23:10 +0100
      Re: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-08 11:10 +0100
        Re: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2017-03-08 15:20 +0100
          Re: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-09 09:30 +0100

#1594437 — [RFC PATCH 0/4 v2] mm: give __GFP_REPEAT a better semantic

FromMichal Hocko <mhocko@kernel.org>
Date2017-03-07 18:00 +0100
Subject[RFC PATCH 0/4 v2] mm: give __GFP_REPEAT a better semantic
Message-ID<tipGN-1c1-19@gated-at.bofh.it>
Hi,
this is a follow up for __GFP_REPEAT clean up merged in 4.7. The previous
version of this patch series was posted as an RFC
http://lkml.kernel.org/r/1465212736-14637-1-git-send-email-mhocko@kernel.org
Since then I have reconsidered the semantic and made it a counterpart
to the __GFP_NORETRY and made it the other extreme end of the retry
logic. Both are not invoking the OOM killer so they are suitable
for allocation paths with a fallback. Also a new potential user has
emerged (kvmalloc - see patch 4). I have also renamed the flag from
__GFP_RETRY_HARD to __GFP_RETRY_MAY_FAIL as this should be more clear.

I have kept the RFC status because of the semantic change. The patch 1
is an exception because it should be merge regardless of the rest.

The main motivation for the change is that the current implementation of
__GFP_REPEAT is not very much useful.

The documentation says:
 * __GFP_REPEAT: Try hard to allocate the memory, but the allocation attempt
 *   _might_ fail.  This depends upon the particular VM implementation.

It just fails to mention that this is true only for large (costly) high
order which has been the case since the flag was introduced. A similar
semantic would be really helpful for smal orders as well, though,
because we have places where a failure with a specific fallback error
handling is preferred to a potential endless loop inside the page
allocator.

The earlier cleanup dropped __GFP_REPEAT usage for low (!costly) order
users so only those which might use larger orders have stayed. One user
which slipped through cracks is addressed in patch 1.

Let's rename the flag to something more verbose and use it for existing
users. Semantic for those will not change. Then implement low (!costly)
orders failure path which is hit after the page allocator is about to
invoke the oom killer. Now we have a good counterpart for __GFP_NORETRY
and finally can tell try as hard as possible without the OOM killer.

Xfs code already has an existing annotation for allocations which are
allowed to fail and we can trivially map them to the new gfp flag
because it will provide the semantic KM_MAYFAIL wants.

kvmalloc will allow also !costly high order allocations to retry hard
before falling back to the vmalloc.

The patchset is based on the current linux-next.

Shortlog
Michal Hocko (4):
      s390: get rid of superfluous __GFP_REPEAT
      mm, tree wide: replace __GFP_REPEAT by __GFP_RETRY_MAYFAIL with more useful semantic
      xfs: map KM_MAYFAIL to __GFP_RETRY_MAYFAIL
      mm: kvmalloc support __GFP_RETRY_MAYFAIL for all sizes

Diffstat
 Documentation/DMA-ISA-LPC.txt                |  2 +-
 arch/powerpc/include/asm/book3s/64/pgalloc.h |  2 +-
 arch/powerpc/kvm/book3s_64_mmu_hv.c          |  2 +-
 arch/s390/mm/pgalloc.c                       |  2 +-
 drivers/mmc/host/wbsd.c                      |  2 +-
 drivers/s390/char/vmcp.c                     |  2 +-
 drivers/target/target_core_transport.c       |  2 +-
 drivers/vhost/net.c                          |  2 +-
 drivers/vhost/scsi.c                         |  2 +-
 drivers/vhost/vsock.c                        |  2 +-
 fs/btrfs/check-integrity.c                   |  2 +-
 fs/btrfs/raid56.c                            |  2 +-
 fs/xfs/kmem.h                                | 10 +++++++++
 include/linux/gfp.h                          | 32 +++++++++++++++++++---------
 include/linux/slab.h                         |  3 ++-
 include/trace/events/mmflags.h               |  2 +-
 mm/hugetlb.c                                 |  4 ++--
 mm/internal.h                                |  2 +-
 mm/page_alloc.c                              | 14 +++++++++---
 mm/sparse-vmemmap.c                          |  4 ++--
 mm/util.c                                    | 14 ++++--------
 mm/vmalloc.c                                 |  2 +-
 mm/vmscan.c                                  |  8 +++----
 net/core/dev.c                               |  6 +++---
 net/core/skbuff.c                            |  2 +-
 net/sched/sch_fq.c                           |  2 +-
 tools/perf/builtin-kmem.c                    |  2 +-
 27 files changed, 78 insertions(+), 53 deletions(-)

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#1594695 — [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT

FromMichal Hocko <mhocko@kernel.org>
Date2017-03-07 23:10 +0100
Subject[PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT
Message-ID<tivsR-5xJ-5@gated-at.bofh.it>
In reply to#1594437
From: Michal Hocko <mhocko@suse.com>

__GFP_REPEAT has a rather weak semantic but since it has been introduced
around 2.6.12 it has been ignored for low order allocations.

page_table_alloc then uses the flag for a single page allocation. This
means that this flag has never been actually useful here because it has
always been used only for PAGE_ALLOC_COSTLY requests.

An earlier attempt to remove the flag 10d58bf297e2 ("s390: get rid of
superfluous __GFP_REPEAT") has missed this one but the situation is very
same here.

Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/s390/mm/pgalloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 995f78532cc2..2776bad61094 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -144,7 +144,7 @@ struct page *page_table_alloc_pgste(struct mm_struct *mm)
 	struct page *page;
 	unsigned long *table;
 
-	page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
+	page = alloc_page(GFP_KERNEL);
 	if (page) {
 		table = (unsigned long *) page_to_phys(page);
 		clear_table(table, _PAGE_INVALID, PAGE_SIZE/2);
-- 
2.11.0

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#1595007 — Re: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT

FromHeiko Carstens <heiko.carstens@de.ibm.com>
Date2017-03-08 11:10 +0100
SubjectRe: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT
Message-ID<tiGHE-55j-17@gated-at.bofh.it>
In reply to#1594695
On Tue, Mar 07, 2017 at 04:48:40PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> __GFP_REPEAT has a rather weak semantic but since it has been introduced
> around 2.6.12 it has been ignored for low order allocations.
> 
> page_table_alloc then uses the flag for a single page allocation. This
> means that this flag has never been actually useful here because it has
> always been used only for PAGE_ALLOC_COSTLY requests.
> 
> An earlier attempt to remove the flag 10d58bf297e2 ("s390: get rid of
> superfluous __GFP_REPEAT") has missed this one but the situation is very
> same here.
> 
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  arch/s390/mm/pgalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

FWIW:
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>

If you want, this can be routed via the s390 tree, whatever you prefer.

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#1595212 — Re: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT

FromMichal Hocko <mhocko@kernel.org>
Date2017-03-08 15:20 +0100
SubjectRe: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT
Message-ID<tiKBA-7HL-13@gated-at.bofh.it>
In reply to#1595007
On Wed 08-03-17 09:23:40, Heiko Carstens wrote:
> On Tue, Mar 07, 2017 at 04:48:40PM +0100, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > __GFP_REPEAT has a rather weak semantic but since it has been introduced
> > around 2.6.12 it has been ignored for low order allocations.
> > 
> > page_table_alloc then uses the flag for a single page allocation. This
> > means that this flag has never been actually useful here because it has
> > always been used only for PAGE_ALLOC_COSTLY requests.
> > 
> > An earlier attempt to remove the flag 10d58bf297e2 ("s390: get rid of
> > superfluous __GFP_REPEAT") has missed this one but the situation is very
> > same here.
> > 
> > Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > ---
> >  arch/s390/mm/pgalloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> FWIW:
> Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Thanks

> If you want, this can be routed via the s390 tree, whatever you prefer.

Yes, that would be great. I suspect the rest will take longer to get
merged or land to a conclusion.

-- 
Michal Hocko
SUSE Labs

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#1595790 — Re: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT

FromHeiko Carstens <heiko.carstens@de.ibm.com>
Date2017-03-09 09:30 +0100
SubjectRe: [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT
Message-ID<tj1Cp-2xk-9@gated-at.bofh.it>
In reply to#1595212
On Wed, Mar 08, 2017 at 03:11:10PM +0100, Michal Hocko wrote:
> On Wed 08-03-17 09:23:40, Heiko Carstens wrote:
> > On Tue, Mar 07, 2017 at 04:48:40PM +0100, Michal Hocko wrote:
> > > From: Michal Hocko <mhocko@suse.com>
> > > 
> > > __GFP_REPEAT has a rather weak semantic but since it has been introduced
> > > around 2.6.12 it has been ignored for low order allocations.
> > > 
> > > page_table_alloc then uses the flag for a single page allocation. This
> > > means that this flag has never been actually useful here because it has
> > > always been used only for PAGE_ALLOC_COSTLY requests.
> > > 
> > > An earlier attempt to remove the flag 10d58bf297e2 ("s390: get rid of
> > > superfluous __GFP_REPEAT") has missed this one but the situation is very
> > > same here.
> > > 
> > > Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> > > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > > ---
> > >  arch/s390/mm/pgalloc.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > FWIW:
> > Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> 
> Thanks
> 
> > If you want, this can be routed via the s390 tree, whatever you prefer.
> 
> Yes, that would be great. I suspect the rest will take longer to get
> merged or land to a conclusion.

Ok, applied. Thanks! :)

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