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Re: [PATCH 01/19] tree wide: get rid of __GFP_REPEAT for order-0 allocations part I

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On Thu 14-04-16 12:56:28, David Rientjes wrote:
> On Mon, 11 Apr 2016, 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. Yet we have
> > the full kernel tree with its usage for apparently order-0 allocations.
> > This is really confusing because __GFP_REPEAT is explicitly documented
> > to allow allocation failures which is a weaker semantic than the current
> > order-0 has (basically nofail).
> > 
> > Let's simply drop __GFP_REPEAT from those places. This would allow
> > to identify place which really need allocator to retry harder and
> > formulate a more specific semantic for what the flag is supposed to do
> > actually.
> > 
> > Cc: linux-arch@vger.kernel.org
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> I did exactly this before, and Andrew objected saying that __GFP_REPEAT 
> may not be needed for the current page allocator's implementation but 
> could with others and that setting __GFP_REPEAT for an allocation 
> provided useful information with regards to intent.

From what I've seen it was more a copy&paste of the arch code which
spread out this flag and there was also a misleading usage.

> At the time, I attempted to eliminate __GFP_REPEAT entirely.

This is not my plan. I actually want to provide a useful semantic for
something like this flag - aka try really hard but eventually fail
for all orders and stop being special only for those that are costly. I
will call it __GFP_BEST_EFFORT. But I have to clean up the current usage
first. Costly orders will keep __GFP_REPEAT because the intent is clear
there. All others will lose the flag and then we can start adding
__GFP_BEST_EFFORT where it matters also for lower orders.
-- 
Michal Hocko
SUSE Labs

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[PATCH 0/19] get rid of superfluous __GFP_REPORT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:10 +0200
  [PATCH 15/19] tile: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:10 +0200
  [PATCH 18/19] crypto: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:10 +0200
    Re: [PATCH 18/19] crypto: get rid of superfluous __GFP_REPEAT Herbert Xu <herbert@gondor.apana.org.au> - 2016-04-14 08:30 +0200
      Re: [PATCH 18/19] crypto: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-14 09:10 +0200
        Re: [PATCH 18/19] crypto: get rid of superfluous __GFP_REPEAT Herbert Xu <herbert@gondor.apana.org.au> - 2016-04-14 10:20 +0200
    [PATCH resend] crypto: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-14 11:00 +0200
      Re: [PATCH resend] crypto: get rid of superfluous __GFP_REPEAT Herbert Xu <herbert@gondor.apana.org.au> - 2016-04-15 16:40 +0200
  [PATCH 09/19] parisc: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:10 +0200
  [PATCH 16/19] unicore32: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:10 +0200
  [PATCH 08/19] nios2: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 01/19] tree wide: get rid of __GFP_REPEAT for order-0 allocations part I Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
    Re: [PATCH 01/19] tree wide: get rid of __GFP_REPEAT for order-0  allocations part I David Rientjes <rientjes@google.com> - 2016-04-14 22:00 +0200
      Re: [PATCH 01/19] tree wide: get rid of __GFP_REPEAT for order-0  allocations part I Michal Hocko <mhocko@kernel.org> - 2016-04-15 09:50 +0200
  [PATCH 06/19] arc: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
    Re: [PATCH 06/19] arc: get rid of superfluous __GFP_REPEAT Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-11 16:30 +0200
  [PATCH 11/19] powerpc: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 10/19] score: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 07/19] mips: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 19/19] jbd2: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 13/19] s390: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
    Re: [PATCH 13/19] s390: get rid of superfluous __GFP_REPEAT Cornelia Huck <cornelia.huck@de.ibm.com> - 2016-04-11 13:30 +0200
      Re: [PATCH 13/19] s390: get rid of superfluous __GFP_REPEAT Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-04-11 14:50 +0200
  [PATCH 12/19] sparc: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 04/19] arm: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
  [PATCH 03/19] x86/efi: get rid of superfluous __GFP_REPEAT Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
    Re: [PATCH 03/19] x86/efi: get rid of superfluous __GFP_REPEAT Matt Fleming <matt@codeblueprint.co.uk> - 2016-04-12 18:00 +0200
  [PATCH 17/19] dm: get rid of superfluous gfp flags Michal Hocko <mhocko@kernel.org> - 2016-04-11 13:20 +0200
    Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Mikulas Patocka <mpatocka@redhat.com> - 2016-04-15 14:30 +0200
      Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Michal Hocko <mhocko@kernel.org> - 2016-04-15 15:10 +0200
        Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Mikulas Patocka <mpatocka@redhat.com> - 2016-04-15 20:50 +0200
          Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Michal Hocko <mhocko@kernel.org> - 2016-04-16 22:40 +0200
            Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Michal Hocko <mhocko@kernel.org> - 2016-04-22 14:50 +0200
              Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Mikulas Patocka <mpatocka@redhat.com> - 2016-04-26 19:30 +0200
                Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Michal Hocko <mhocko@kernel.org> - 2016-04-27 10:40 +0200
  CC in git cover letter vs patches (was Re: [PATCH 0/19] get rid of  superfluous __GFP_REPORT) Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-04-13 13:30 +0200
    Re: CC in git cover letter vs patches (was Re: [PATCH 0/19] get rid  of superfluous __GFP_REPORT) Michal Hocko <mhocko@kernel.org> - 2016-04-13 15:40 +0200

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