Re: [PATCH 0/5] Speed up mremap on large regions

On Wed, Sep 30, 2020 at 10:21:17PM +0000, Kalesh Singh wrote:

mremap time can be optimized by moving entries at the PMD/PUD level if the source and destination addresses are PMD/PUD-aligned and PMD/PUD-sized. Enable moving at the PMD and PUD levels on arm64 and x86. Other architectures where this type of move is supported and known to be safe can also opt-in to these optimizations by enabling HAVE_MOVE_PMD and HAVE_MOVE_PUD.

Observed Performance Improvements for remapping a PUD-aligned 1GB-sized region on x86 and arm64:

- HAVE_MOVE_PMD is already enabled on x86 : N/A
- Enabling HAVE_MOVE_PUD on x86   : ~13x speed up

- Enabling HAVE_MOVE_PMD on arm64 : ~ 8x speed up
- Enabling HAVE_MOVE_PUD on arm64 : ~19x speed up

      Altogether, HAVE_MOVE_PMD and HAVE_MOVE_PUD
      give a total of ~150x speed up on arm64.

Is there a *real* workload that benefit from HAVE_MOVE_PUD?