Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers
Date	2017-01-19 11:00 +0100
Message-ID	<t1hFE-8hK-17@gated-at.bofh.it> (permalink)
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On Thu 19-01-17 01:09:35, John Hubbard wrote:
[...]
> So that leaves us with maybe this for documentation?
> 
>  * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL should not be passed in.
>  * Passing in __GFP_REPEAT is supported, and will cause the following behavior:
>  * for larger (>64KB) allocations, the first part (kmalloc) will do some
>  * retrying, before falling back to vmalloc.

I am worried this is just too vague. It doesn't really help user to
decide whether "do some retrying" is what he really want's or needs.

So I would rather see the following.
"
 * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported. __GFP_REPEAT
 * is supported only for large (>32kB) allocations and it should be used when using
 * kmalloc is preferable because vmalloc fallback has visible performance drawbacks.
"

I would also add
"
Any use of gfp flags outside of GFP_KERNEL should be consulted with mm people.
"

Does it sound any better?
-- 
Michal Hocko
SUSE Labs

Thread

Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-01-16 20:50 +0100
  Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers John Hubbard <jhubbard@nvidia.com> - 2017-01-16 22:30 +0100
    Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-01-16 22:50 +0100
      Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers John Hubbard <jhubbard@nvidia.com> - 2017-01-16 23:00 +0100
        Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-01-17 09:00 +0100
          Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers John Hubbard <jhubbard@nvidia.com> - 2017-01-18 07:10 +0100
            Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-01-18 09:30 +0100
              Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers John Hubbard <jhubbard@nvidia.com> - 2017-01-19 09:40 +0100
                Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-01-19 10:10 +0100
                Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers John Hubbard <jhubbard@nvidia.com> - 2017-01-19 10:20 +0100
                Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers Michal Hocko <mhocko@kernel.org> - 2017-01-19 11:00 +0100
                Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers John Hubbard <jhubbard@nvidia.com> - 2017-01-19 22:30 +0100

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