From: Roland Mainz <roland.mainz@nrubsig.org>
To: linux-nfs@vger.kernel.org
Cc: Chuck Lever <cel@kernel.org>
Subject: Re: [PATCH] NFSD: Increase the default max_block_size to 4MB
Date: Mon, 20 Apr 2026 23:25:39 +0200 [thread overview]
Message-ID: <CAKAoaQnN16S6Lh0sgCXF7bLB6sxTSxqCjr-RNt69f6YWyiv6iQ@mail.gmail.com> (raw)
In-Reply-To: <20260420153830.463215-1-cel@kernel.org>
On Mon, Apr 20, 2026 at 5:38 PM Chuck Lever <cel@kernel.org> wrote:
>
> From: Chuck Lever <chuck.lever@oracle.com>
>
> Commit 8a81f16de64f ("NFSD: Add a "default" block size") introduced
> NFSSVC_DEFBLKSIZE at 1MB, well below the 4MB NFSSVC_MAXBLKSIZE
> ceiling, with the stated intent that a later change would raise the
> default.
>
> Raising the default reduces per-RPC overhead on fast networks by
> amortizing header processing and scheduling costs across larger
> payloads. The halving loop in nfsd_get_default_max_blksize()
> constrains the returned value to 1/4096 of available RAM, so the
> new 4MB default takes effect only on systems with at least 16GB of
> RAM. Smaller machines continue to receive the same computed value
> as before. Administrators can still override the computed value
> through /proc/fs/nfsd/max_block_size.
>
> On systems where the new default takes effect,
> svc_sock_setbufsize() sizes each service socket's send and receive
> buffers as nreqs * max_mesg * 2. Quadrupling max_mesg therefore
> quadruples the per-socket buffer reservation at a fixed thread
> count, which operators tuning large thread pools should account
> for.
>
> Note well: Your NFS client implementation must support large read
> and write size settings to benefit from this change.
>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> fs/nfsd/nfsd.h | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index a01d70953358..daa63c1b161c 100644
> --- a/fs/nfsd/nfsd.h
> +++ b/fs/nfsd/nfsd.h
> @@ -45,11 +45,10 @@ bool nfsd_support_version(int vers);
>
> /*
> * Default and maximum payload size (NFS READ or WRITE), in bytes.
> - * The default is historical, and the maximum is an implementation
> - * limit.
> + * The maximum is an implementation limit.
> */
> enum {
> - NFSSVC_DEFBLKSIZE = 1 * 1024 * 1024,
> + NFSSVC_DEFBLKSIZE = 4 * 1024 * 1024,
> NFSSVC_MAXBLKSIZE = RPCSVC_MAXPAYLOAD,
> };
Works with ms-nfs41-client.
Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
----
Bye,
Roland
--
__ . . __
(o.\ \/ /.o) roland.mainz@nrubsig.org
\__\/\/__/ MPEG specialist, C&&JAVA&&Sun&&Unix programmer
/O /==\ O\ TEL +49 641 3992797
(;O/ \/ \O;)
prev parent reply other threads:[~2026-04-20 21:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-20 15:38 [PATCH] NFSD: Increase the default max_block_size to 4MB Chuck Lever
2026-04-20 17:12 ` Jeff Layton
2026-04-20 21:25 ` Roland Mainz [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKAoaQnN16S6Lh0sgCXF7bLB6sxTSxqCjr-RNt69f6YWyiv6iQ@mail.gmail.com \
--to=roland.mainz@nrubsig.org \
--cc=cel@kernel.org \
--cc=linux-nfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).