Re: [PATCH v2 02/10] sunrpc: Add a helper to derive maxpages from sv_max_mesg

[Chuck Lever <cel@kernel.org>]

On 4/22/25 4:48 PM, NeilBrown wrote:
> On Sun, 20 Apr 2025, cel@kernel.org wrote:
>> From: Chuck Lever <chuck.lever@oracle.com>
>>
>> This page count is to be used to allocate various arrays of pages,
>> bio_vecs, and kvecs, replacing the fixed RPCSVC_MAXPAGES value.
>>
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>>  include/linux/sunrpc/svc.h | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
>> index 74658cca0f38..5b879c31d7b8 100644
>> --- a/include/linux/sunrpc/svc.h
>> +++ b/include/linux/sunrpc/svc.h
>> @@ -159,6 +159,18 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
>>  #define RPCSVC_MAXPAGES		((RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE \
>>  				+ 2 + 1)
>>  
>> +/**
>> + * svc_serv_maxpages - maximum pages/kvecs needed for one RPC message
>> + * @serv: RPC service context
>> + *
>> + * Returns a count of pages or vectors that can hold the maximum
>> + * size RPC message for @serv.
>> + */
>> +static inline unsigned long svc_serv_maxpages(const struct svc_serv *serv)
>> +{
>> +	return ((serv->sv_max_mesg + PAGE_SIZE - 1) >> PAGE_SHIFT) + 2 + 1;
>> +}
>> +
> 
> This looks like it should be
>      DIV_ROUND_UP(serv->sv_max_mesg, PAGE_SIZE) + 2

Fair enough! I had forgotten about that macro.


> Could we document what the "+ 2" is for??

10/10 in this series moves an existing documenting comment for that
purpose. I've relocated that hunk to this patch, but I think the text
needs to be revisited because it ignores NFSv4 COMPOUNDs that may
carry multiple payloads.

I plan to post a v3 of this series soon.


> Thanks,
> NeilBrown
> 
> 
>>  /*
>>   * The context of a single thread, including the request currently being
>>   * processed.
>> -- 
>> 2.49.0
>>
>>
> 


-- 
Chuck Lever