linux-kernel - Re: [PATCH v1 0/3] Improve hugetlbfs read on HWPOISON hugepages

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Date:   Wed, 17 May 2023 16:30:20 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Jiaqi Yan <jiaqiyan@...gle.com>
Cc:     songmuchun@...edance.com, naoya.horiguchi@....com,
        shy828301@...il.com, linmiaohe@...wei.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, duenwen@...gle.com,
        axelrasmussen@...gle.com, jthoughton@...gle.com
Subject: Re: [PATCH v1 0/3] Improve hugetlbfs read on HWPOISON hugepages

On 05/17/23 16:09, Jiaqi Yan wrote:
> Today when hardware memory is corrupted in a hugetlb hugepage,
> kernel leaves the hugepage in pagecache [1]; otherwise future mmap or
> read will suject to silent data corruption. This is implemented by
> returning -EIO from hugetlb_read_iter immediately if the hugepage has
> HWPOISON flag set.
> 
> Since memory_failure already tracks the raw HWPOISON subpages in a
> hugepage, a natural improvement is possible: if userspace only asks for
> healthy subpages in the pagecache, kernel can return these data.

Thanks for putting this together.

I recall discussing this some time back, and deciding to wait and see
how HGM would progress.  Since it may be some time before HGM goes
upstream, it would be reasonable to consider this again.

One quick question.
Do you have an actual use case for this?  It certainly is an improvement
over existing functionality.  However, I am not aware of too many (?any?)
users actually doing read() calls on hugetlb files.
-- 
Mike Kravetz

> This patchset implements this improvement. It consist of three parts.
> The 1st commit exports the functionality to tell if a subpage inside a
> hugetlb hugepage is a raw HWPOISON page. The 2nd commit teaches
> hugetlbfs_read_iter to return as many healthy bytes as possible.
> The 3rd commit properly tests this new feature.
> 
> [1] commit 8625147cafaa ("hugetlbfs: don't delete error page from pagecache")
> 
> Jiaqi Yan (3):
>   mm/hwpoison: find subpage in hugetlb HWPOISON list
>   hugetlbfs: improve read HWPOISON hugepage
>   selftests/mm: add tests for HWPOISON hugetlbfs read
> 
>  fs/hugetlbfs/inode.c                          |  62 +++-
>  include/linux/mm.h                            |  23 ++
>  mm/memory-failure.c                           |  26 +-
>  tools/testing/selftests/mm/.gitignore         |   1 +
>  tools/testing/selftests/mm/Makefile           |   1 +
>  .../selftests/mm/hugetlb-read-hwpoison.c      | 322 ++++++++++++++++++
>  6 files changed, 419 insertions(+), 16 deletions(-)
>  create mode 100644 tools/testing/selftests/mm/hugetlb-read-hwpoison.c
> 
> -- 
> 2.40.1.606.ga4b1b128d6-goog
>