Re: [PATCH v1 3/3] selftests/mm: Speed up split_huge_page_test

[Peter Xu <peterx@redhat.com>]

On Tue, Mar 18, 2025 at 05:43:41PM +0000, Ryan Roberts wrote:
> create_pagecache_thp_and_fd() was previously writing a file sized at
> twice the PMD size by making a per-byte write syscall. This was quite
> slow when the PMD size is 4M, but completely intolerable for 32M (PMD
> size for arm64's 16K page size), and 512M (PMD size for arm64's 64K page
> size).
> 
> The byte pattern has a 256 byte period, so let's create a 1K buffer and
> fill it with exactly 4 periods. Then we can write the buffer as many
> times as is required to fill the file. This makes things much more
> tolerable.
> 
> The test now passes for 16K page size. It still fails for 64K page size
> because MAX_PAGECACHE_ORDER is too small for 512M folio size (I think).
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Acked-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu