Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure

From	Dave Hansen <dave.hansen@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure
Date	2017-03-24 15:00 +0100
Message-ID	<toxV0-2ms-3@gated-at.bofh.it> (permalink)
References	(3 earlier) <top1o-4qf-5@gated-at.bofh.it> <topup-4DO-1@gated-at.bofh.it> <torcR-5YR-9@gated-at.bofh.it> <torFU-6sZ-19@gated-at.bofh.it> <torZg-6BK-29@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On 03/24/2017 12:33 AM, John Hubbard wrote:
> There might be some additional information you are using to come up with
> that conclusion, that is not obvious to me. Any thoughts there? These
> calls use the same underlying page allocator (and I thought that both
> were subject to the same constraints on defragmentation, as a result of
> that). So I am not seeing any way that kmalloc could possibly be a
> less-fragmenting call than vmalloc.

You guys are having quite a discussion over a very small point.

But, Ying is right.

Let's say we have a two-page data structure.  vmalloc() takes two
effectively random order-0 pages, probably from two different 2M pages
and pins them.  That "kills" two 2M pages.

kmalloc(), allocating two *contiguous* pages, is very unlikely to cross
a 2M boundary (it theoretically could).  That means it will only "kill"
the possibility of a single 2M page.  More 2M pages == less fragmentation.

Thread

[PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure "Huang, Ying" <ying.huang@intel.com> - 2017-03-20 10:00 +0100
  [PATCH -v2 2/2] mm, swap: Sort swap entries before free "Huang, Ying" <ying.huang@intel.com> - 2017-03-20 10:00 +0100
  Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap  data structure David Rientjes <rientjes@google.com> - 2017-03-20 22:40 +0100
    Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure "Huang\, Ying" <ying.huang@intel.com> - 2017-03-24 03:50 +0100
      Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data  structure John Hubbard <jhubbard@nvidia.com> - 2017-03-24 05:30 +0100
        Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure "Huang\, Ying" <ying.huang@intel.com> - 2017-03-24 06:00 +0100
          Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data  structure John Hubbard <jhubbard@nvidia.com> - 2017-03-24 07:50 +0100
            Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure "Huang\, Ying" <ying.huang@intel.com> - 2017-03-24 08:20 +0100
              Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data  structure John Hubbard <jhubbard@nvidia.com> - 2017-03-24 08:40 +0100
                Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data  structure Dave Hansen <dave.hansen@linux.intel.com> - 2017-03-24 15:00 +0100
                Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap  data structure Tim Chen <tim.c.chen@linux.intel.com> - 2017-03-24 18:00 +0100
                Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data  structure John Hubbard <jhubbard@nvidia.com> - 2017-03-24 19:20 +0100

csiph-web