linux-kernel - Re: [PATCH] NFS: Convert kmap_atomic() to kmap_local

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Message-ID: <CAFX2Jfmz9pqPUyqr6Dy-ELu+1SGaKmpk4hNkN+LoK4xNFM1XHA@mail.gmail.com>
Date:   Wed, 3 May 2023 16:57:27 -0400
From:   Anna Schumaker <anna@...nel.org>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Trond Myklebust <trond.myklebust@...merspace.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH] NFS: Convert kmap_atomic() to kmap_local_folio()

On Wed, May 3, 2023 at 1:24 PM Fabio M. De Francesco
<fmdefrancesco@...il.com> wrote:
>
> kmap_atomic() is deprecated in favor of kmap_local_{folio,page}().
>
> Therefore, replace kmap_atomic() with kmap_local_folio() in
> nfs_readdir_folio_array_append().
>
> kmap_atomic() disables page-faults and preemption (the latter only for
> !PREEMPT_RT kernels), However, the code within the mapping/un-mapping in
> nfs_readdir_folio_array_append() does not depend on the above-mentioned
> side effects.
>
> Therefore, a mere replacement of the old API with the new one is all that
> is required (i.e., there is no need to explicitly add any calls to
> pagefault_disable() and/or preempt_disable()).
>
> Tested with (x)fstests in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel
> with HIGHMEM64GB enabled.

Thanks Fabio! Looks like I missed this when I wrote: ec108d3cc766
("NFS: Convert readdir page array functions to use a folio")

I have it applied now.

Anna

>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>
> "./check -nfs -g quick", with or without this patch, always fails the
> same 12 tests of 559: generic/053 generic/099 generic/105 generic/193
> generic/294 generic/318 generic/319 generic/444 generic/465 generic/528
> generic/529 generic/531.
>
> Therefore, I think I can say that this patch does not introduce any
> regressions.
>
>  fs/nfs/dir.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 8257de6dba45..8fa8ae49d6cd 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -317,7 +317,7 @@ static int nfs_readdir_folio_array_append(struct folio *folio,
>
>         name = nfs_readdir_copy_name(entry->name, entry->len);
>
> -       array = kmap_atomic(folio_page(folio, 0));
> +       array = kmap_local_folio(folio, 0);
>         if (!name)
>                 goto out;
>         ret = nfs_readdir_array_can_expand(array);
> @@ -340,7 +340,7 @@ static int nfs_readdir_folio_array_append(struct folio *folio,
>                 nfs_readdir_array_set_eof(array);
>  out:
>         *cookie = array->last_cookie;
> -       kunmap_atomic(array);
> +       kunmap_local(array);
>         return ret;
>  }
>
> --
> 2.40.0
>