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Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was "zram: do not use copy_page with non-page alinged address")

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On Thu, Apr 20, 2017 at 10:45:42AM +0900, Sergey Senozhatsky wrote:
> On (04/19/17 04:51), Matthew Wilcox wrote:
> [..]
> > > > > Another approach is the API does normal thing for non-aligned prefix and
> > > > > tail space and fast thing for aligned space.
> > > > > Otherwise, it would be happy if the API has WARN_ON non-page SIZE aligned
> > > > > address.
> > 
> > Why not just use memcpy()?  Is copy_page() significantly faster than
> > memcpy() for a PAGE_SIZE amount of data?
> 
> that's a good point.
> 
> I was going to ask yesterday - do we even need copy_page()? arch that
> provides well optimized copy_page() quite likely provides somewhat
> equally optimized memcpy(). so may be copy_page() is not even needed?

I don't know.

Just I found https://download.samba.org/pub/paulus/ols-2003-presentation.pdf
and heard https://lkml.org/lkml/2017/4/10/1270.

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copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was "zram:  do not use copy_page with non-page alinged address") Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 03:50 +0200
  Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Christoph Lameter <cl@linux.com> - 2017-04-17 17:30 +0200
    Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Minchan Kim <minchan@kernel.org> - 2017-04-18 02:10 +0200
      Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Michal Hocko <mhocko@kernel.org> - 2017-04-18 09:40 +0200
        Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Michal Hocko <mhocko@kernel.org> - 2017-04-18 13:10 +0200
          Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-19 08:20 +0200
        Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-18 13:10 +0200
        Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Minchan Kim <minchan@kernel.org> - 2017-04-19 08:10 +0200
          Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Matthew Wilcox <willy@infradead.org> - 2017-04-19 14:00 +0200
            Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-20 03:50 +0200
              Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Minchan Kim <minchan@kernel.org> - 2017-04-20 09:00 +0200
    Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-18 12:50 +0200
      Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Christoph Lameter <cl@linux.com> - 2017-04-18 15:30 +0200
    Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was  "zram: do not use copy_page with non-page alinged address") Matthew Wilcox <willy@infradead.org> - 2017-04-18 15:20 +0200

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