Re: [PATCH v4 00/14] Allocate payload arrays dynamically

Zhu Yanjun
2025-04-29T13:52:27Z

On 29.04.25 15:41, Chuck Lever wrote:
> On 4/29/25 9:06 AM, Zhu Yanjun wrote:
>> On 28.04.25 21:36, cel@kernel.org wrote:
>>> From: Chuck Lever <chuck.lever@oracle.com>
>>>
>>> In order to make RPCSVC_MAXPAYLOAD larger (or variable in size), we
>>> need to do something clever with the payload arrays embedded in
>>> struct svc_rqst and elsewhere.
>>>
>>> My preference is to keep these arrays allocated all the time because
>>> allocating them on demand increases the risk of a memory allocation
>>> failure during a large I/O. This is a quick-and-dirty approach that
>>> might be replaced once NFSD is converted to use large folios.
>>>
>>> The downside of this design choice is that it pins a few pages per
>>> NFSD thread (and that's the current situation already). But note
>>> that because RPCSVC_MAXPAGES is 259, each array is just over a page
>>> in size, making the allocation waste quite a bit of memory beyond
>>> the end of the array due to power-of-2 allocator round up. This gets
>>> worse as the MAXPAGES value is doubled or quadrupled.
>>>
>>> This series also addresses similar issues in the socket and RDMA
>>> transports.
>>>
>>> v4 is "code complete", unless there are new code change requests.
>>> I'm not convinced that adding XDR pad alignment to svc_reserve()
>>> is good, but I'm willing to consider it further.
>>>
>>> It turns out there is already a tuneable for the maximum read and
>>> write size in NFSD:
>>>
>>>    /proc/fs/nfsd/max_block_size
>> Hi,
>>
>> Based on the head commit ca91b9500108 Merge tag 'v6.15-rc4-ksmbd-server-
>> fixes' of git://git.samba.org/ksmbd, I applied this patch series.
>>
>> When I built the kernel, the following error will pop out.
>> "
>> In file included from ./arch/x86/include/asm/bug.h:103,
>>                  from ./include/linux/bug.h:5,
>>                  from ./arch/x86/include/asm/paravirt.h:19,
>>                  from ./arch/x86/include/asm/irqflags.h:102,
>>                  from ./include/linux/irqflags.h:18,
>>                  from ./include/linux/spinlock.h:59,
>>                  from ./include/linux/fs_struct.h:6,
>>                  from fs/nfsd/nfs4proc.c:35:
>> fs/nfsd/nfs4proc.c: In function ‘nfsd4_write’:
>> ./include/linux/array_size.h:11:38: warning: division ‘sizeof (struct
>> kvec *) / sizeof (struct kvec)’ does not compute the number of array
>> elements [-Wsizeof-pointer-div]
>>    11 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
>> __must_be_array(arr))
>>       |                                      ^
>> ./include/asm-generic/bug.h:111:32: note: in definition of macro
>> ‘WARN_ON_ONCE’
>>   111 |         int __ret_warn_on = !!(condition);                      \
>>       |                                ^~~~~~~~~
>> fs/nfsd/nfs4proc.c:1231:30: note: in expansion of macro ‘ARRAY_SIZE’
>>  1231 |         WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec));
>>       |                              ^~~~~~~~~~
>> ./include/linux/compiler.h:197:62: error: static assertion failed: "must
>> be array"
>>   197 | #define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct
>> {_Static_assert(!(e), msg);}))
>>       | ^~~~~~~~~~~~~~
>> ./include/asm-generic/bug.h:111:32: note: in definition of macro
>> ‘WARN_ON_ONCE’
>>   111 |         int __ret_warn_on = !!(condition);                      \
>>       |                                ^~~~~~~~~
>> ./include/linux/compiler.h:202:33: note: in expansion of macro
>> ‘__BUILD_BUG_ON_ZERO_MSG’
>>   202 | #define __must_be_array(a) __BUILD_BUG_ON_ZERO_MSG(!
>> __is_array(a), \
>>       |                                 ^~~~~~~~~~~~~~~~~~~~~~~
>> ./include/linux/array_size.h:11:59: note: in expansion of macro
>> ‘__must_be_array’
>>    11 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
>> __must_be_array(arr))
>>       | ^~~~~~~~~~~~~~~
>> fs/nfsd/nfs4proc.c:1231:30: note: in expansion of macro ‘ARRAY_SIZE’
>>  1231 |         WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec));
>>       |                              ^~~~~~~~~~
>> make[4]: *** [scripts/Makefile.build:203: fs/nfsd/nfs4proc.o] Error 1
>> make[4]: *** Waiting for unfinished jobs....
>> make[3]: *** [scripts/Makefile.build:461: fs/nfsd] Error 2
>> make[3]: *** Waiting for unfinished jobs....
>> make[2]: *** [scripts/Makefile.build:461: fs] Error 2
>> make[2]: *** Waiting for unfinished jobs....
>> make[1]: *** [/home/zyanjun/Development/github-linux/Makefile:2011: .]
>> Error 2
>> make: *** [Makefile:248: __sub-make] Error 2
>> "
> The patches actually are to be applied to nfsd-testing, which has a
> patch that removes the errant WARN_ON_ONCE.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/commit/?h=nfsd-testing&id=a356997303fbea4914bfbdad9645c61d88b28c4d
>
> If you apply that one-liner first, then this series, it should compile
> properly.

Thanks. Great.

Follow your advice, the patch series can compile properly.

Best Regards,

Zhu Yanjun

>
>
>> The building host is as below:
>>
>> $ cat /etc/issue.net
>> Ubuntu 22.04.5 LTS
>>
>> $ gcc --version
>> gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
>> Copyright (C) 2021 Free Software Foundation, Inc.
>> This is free software; see the source for copying conditions.  There is NO
>> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>>
>> $ uname -a
>> Linux lb03055 6.8.0-58-generic #60~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC
>> Fri Mar 28 16:09:21 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
>>
>>
>> Zhu Yanjun
>>
>>> Since there is an existing user space API for this, my initial
>>> arguments against adding a tuneable are moot. max_block_size should
>>> be adequate for this purpose, and enabling it to be set to larger
>>> values should not impact the kernel-user space API in any way.
>>>
>>> Changes since v3:
>>> * Improved the rdma_rw context count estimate
>>> * Dropped "NFSD: Remove NFSSVC_MAXBLKSIZE from .pc_xdrressize"
>>> * Cleaned up the max size macros a bit
>>> * Completed the implementation of adjustable max_block_size
>>>
>>> Changes since v2:
>>> * Address Jeff's review comments
>>> * Address Neil's review comments
>>> * Start removing a few uses of NFSSVC_MAXBLKSIZE
>>>
>>> Chuck Lever (14):
>>>    svcrdma: Reduce the number of rdma_rw contexts per-QP
>>>    sunrpc: Add a helper to derive maxpages from sv_max_mesg
>>>    sunrpc: Remove backchannel check in svc_init_buffer()
>>>    sunrpc: Replace the rq_pages array with dynamically-allocated memory
>>>    sunrpc: Replace the rq_vec array with dynamically-allocated memory
>>>    sunrpc: Replace the rq_bvec array with dynamically-allocated memory
>>>    sunrpc: Adjust size of socket's receive page array dynamically
>>>    svcrdma: Adjust the number of entries in svc_rdma_recv_ctxt::rc_pages
>>>    svcrdma: Adjust the number of entries in svc_rdma_send_ctxt::sc_pages
>>>    sunrpc: Remove the RPCSVC_MAXPAGES macro
>>>    NFSD: Remove NFSD_BUFSIZE
>>>    NFSD: Remove NFSSVC_MAXBLKSIZE_V2 macro
>>>    NFSD: Add a "default" block size
>>>    SUNRPC: Bump the maximum payload size for the server
>>>
>>>   fs/nfsd/nfs4proc.c                       |  2 +-
>>>   fs/nfsd/nfs4state.c                      |  2 +-
>>>   fs/nfsd/nfs4xdr.c                        |  2 +-
>>>   fs/nfsd/nfsd.h                           | 24 ++++-------
>>>   fs/nfsd/nfsproc.c                        |  4 +-
>>>   fs/nfsd/nfssvc.c                         |  2 +-
>>>   fs/nfsd/nfsxdr.c                         |  4 +-
>>>   fs/nfsd/vfs.c                            |  2 +-
>>>   include/linux/sunrpc/svc.h               | 45 +++++++++++++--------
>>>   include/linux/sunrpc/svc_rdma.h          |  6 ++-
>>>   include/linux/sunrpc/svcsock.h           |  4 +-
>>>   net/sunrpc/svc.c                         | 51 +++++++++++++++---------
>>>   net/sunrpc/svc_xprt.c                    | 10 +----
>>>   net/sunrpc/svcsock.c                     | 15 ++++---
>>>   net/sunrpc/xprtrdma/svc_rdma_recvfrom.c  |  8 +++-
>>>   net/sunrpc/xprtrdma/svc_rdma_rw.c        |  2 +-
>>>   net/sunrpc/xprtrdma/svc_rdma_sendto.c    | 16 ++++++--
>>>   net/sunrpc/xprtrdma/svc_rdma_transport.c | 14 ++++---
>>>   18 files changed, 122 insertions(+), 91 deletions(-)
>>>
>
--
Best Regards,
Yanjun.Zhu