linux-kernel - Re: [PATCH 1/2] Revert "page cache: fix page_cache_next/prev

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Date:   Wed, 21 Jun 2023 15:18:55 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH 1/2] Revert
 "page cache: fix page_cache_next/prev_miss off by one"

On Wed, 21 Jun 2023 14:24:02 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> This reverts commit 9425c591e06a9ab27a145ba655fb50532cf0bcc9
> 
> The reverted commit fixed up routines primarily used by readahead code
> such that they could also be used by hugetlb.  Unfortunately, this
> caused a performance regression as pointed out by the Closes: tag.
> 
> The hugetlb code which uses page_cache_next_miss will be addressed in
> a subsequent patch.

Often these throughput changes are caused by rather random
alignment/layout changes and the code change itself was innocent.

Do we have an explanation for this regression, or was it a surprise?