Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64

[Anshuman Khandual]

On 09/07/2016 10:16 PM, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
> 
> In this patch, the size of the swap cluster is changed to that of the
> THP (Transparent Huge Page) on x86_64 architecture (512).  This is for
> the THP swap support on x86_64.  Where one swap cluster will be used to
> hold the contents of each THP swapped out.  And some information of the
> swapped out THP (such as compound map count) will be recorded in the
> swap_cluster_info data structure.
> 
> For other architectures which want THP swap support, THP_SWAP_CLUSTER
> need to be selected in the Kconfig file for the architecture.
> 
> In effect, this will enlarge swap cluster size by 2 times on x86_64.
> Which may make it harder to find a free cluster when the swap space
> becomes fragmented.  So that, this may reduce the continuous swap space
> allocation and sequential write in theory.  The performance test in 0day
> shows no regressions caused by this.

This patch needs to be split into two separate ones

(1) Add THP_SWAP_CLUSTER config option
(2) Enable CONFIG_THP_SWAP_CLUSTER for X86_64

The first patch should explain the proposal and the second patch
should have 86_64 arch specific details, regressions etc as already
been explained in the commit message.