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

[Kirill A. Shutemov]

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?

-- 
 Kirill A. Shutemov