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Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt

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Hi Andrew,

On Fri, Jul 28, 2017 at 02:21:23PM -0700, Andrew Morton wrote:
> On Fri, 28 Jul 2017 10:31:43 -0700 Matthew Wilcox <willy@infradead.org> wrote:
> 
> > On Fri, Jul 28, 2017 at 10:56:01AM -0600, Ross Zwisler wrote:
> > > Dan Williams and Christoph Hellwig have recently expressed doubt about
> > > whether the rw_page() interface made sense for synchronous memory drivers
> > > [1][2].  It's unclear whether this interface has any performance benefit
> > > for these drivers, but as we continue to fix bugs it is clear that it does
> > > have a maintenance burden.  This series removes the rw_page()
> > > implementations in brd, pmem and btt to relieve this burden.
> > 
> > Why don't you measure whether it has performance benefits?  I don't
> > understand why zram would see performance benefits and not other drivers.
> > If it's going to be removed, then the whole interface should be removed,
> > not just have the implementations removed from some drivers.
> 
> Yes please.  Minchan, could you please take a look sometime?

rw_page's gain is reducing of dynamic allocation in swap path
as well as performance gain thorugh avoiding bio allocation.
And it would be important in memory pressure situation.

I guess it comes from bio_alloc mempool. Usually, zram-swap works
in high memory pressure so mempool would be exahusted easily.
It means that mempool wait and repeated alloc would consume the
overhead.

Actually, at that time although Karam reported the gain is 2.4%,
I got a report from production team that the gain in corner case
(e.g., animation playing is smooth) would be much higher than
expected.

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[PATCH 0/3] remove rw_page() from brd, pmem and btt Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-07-28 19:00 +0200
  [PATCH 1/3] btt: remove btt_rw_page() Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-07-28 19:00 +0200
  [PATCH 2/3] pmem: remove pmem_rw_page() Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-07-28 19:10 +0200
  [PATCH 3/3] brd: remove brd_rw_page() Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-07-28 19:10 +0200
  Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Matthew Wilcox <willy@infradead.org> - 2017-07-28 19:40 +0200
    Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Andrew Morton <akpm@linux-foundation.org> - 2017-07-28 23:30 +0200
      Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-07-31 00:20 +0200
        Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-07-31 00:40 +0200
        Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Christoph Hellwig <hch@lst.de> - 2017-07-31 09:20 +0200
          Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-07-31 09:50 +0200
            Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Christoph Hellwig <hch@lst.de> - 2017-07-31 09:50 +0200
              Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-08-01 08:30 +0200
            Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Christoph Hellwig <hch@lst.de> - 2017-07-31 09:50 +0200
    Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-08-03 00:20 +0200
      Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-08-03 02:20 +0200
        Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Dan Williams <dan.j.williams@intel.com> - 2017-08-03 02:40 +0200
        Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Christoph Hellwig <hch@lst.de> - 2017-08-03 10:10 +0200
          Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-08-04 03:00 +0200
        Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-08-03 23:20 +0200
          Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Jens Axboe <axboe@kernel.dk> - 2017-08-03 23:20 +0200
          Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-08-04 06:00 +0200
            Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-08-04 10:20 +0200
              Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Dan Williams <dan.j.williams@intel.com> - 2017-08-04 20:10 +0200
                Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Ross Zwisler <ross.zwisler@linux.intel.com> - 2017-08-04 20:30 +0200
                Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Dan Williams <dan.j.williams@intel.com> - 2017-08-04 20:30 +0200
                Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt Minchan Kim <minchan@kernel.org> - 2017-08-07 10:30 +0200

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