Re: [RFC PATCH v1 21/57] sunrpc: Remove PAGE_SIZE compile-time constant assumption

Ryan Roberts
2024-10-16T15:11:10Z

On 16/10/2024 15:54, Jeff Layton wrote:
> On Wed, 2024-10-16 at 10:47 -0400, Chuck Lever wrote:
>> On Wed, Oct 16, 2024 at 03:42:12PM +0100, Ryan Roberts wrote:
>>> + Chuck Lever, Jeff Layton
>>>
>>> This was a rather tricky series to get the recipients correct for and my script
>>> did not realize that "supporter" was a pseudonym for "maintainer" so you were
>>> missed off the original post. Appologies!
>>>
>>> More context in cover letter:
>>> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
>>>
>>>
>>> On 14/10/2024 11:58, Ryan Roberts wrote:
>>>> To prepare for supporting boot-time page size selection, refactor code
>>>> to remove assumptions about PAGE_SIZE being compile-time constant. Code
>>>> intended to be equivalent when compile-time page size is active.
>>>>
>>>> Updated array sizes in various structs to contain enough entries for the
>>>> smallest supported page size.
>>>>
>>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>>> ---
>>>>
>>>> ***NOTE***
>>>> Any confused maintainers may want to read the cover note here for context:
>>>> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
>>>>
>>>> include/linux/sunrpc/svc.h | 8 +++++---
>>>> include/linux/sunrpc/svc_rdma.h | 4 ++--
>>>> include/linux/sunrpc/svcsock.h | 2 +-
>>>> 3 files changed, 8 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
>>>> index a7d0406b9ef59..dda44018b8f36 100644
>>>> --- a/include/linux/sunrpc/svc.h
>>>> +++ b/include/linux/sunrpc/svc.h
>>>> @@ -160,6 +160,8 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
>>>> */
>>>> #define RPCSVC_MAXPAGES ((RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE \
>>>> + 2 + 1)
>>>> +#define RPCSVC_MAXPAGES_MAX ((RPCSVC_MAXPAYLOAD+PAGE_SIZE_MIN-1)/PAGE_SIZE_MIN \
>>>> + + 2 + 1)
>>
>> There is already a "MAX" in the name, so adding this new macro seems
>> superfluous to me. Can we get away with simply updating the
>> "RPCSVC_MAXPAGES" macro, instead of adding this new one?
>>
>
> +1 that was my thinking too. This is mostly just used to size arrays,
> so we might as well just change the existing macro.

I agree, its not the prettiest. I was (incorrectly) assuming you would want to
continue to limit the number of actual pages at runtime based on the in-use page
size. That said, looking again at the code, RPCSVC_MAXPAGES never actually gets
used to dynamically allocate any memory. So I propose to just do the following:

#define RPCSVC_MAXPAGES ((RPCSVC_MAXPAYLOAD+PAGE_SIZE_MIN-1)/
PAGE_SIZE_MIN + 2 + 1)

That will be 259 in practice (assuming PAGE_SIZE_MIN=4K).

>
> With 64k pages we probably wouldn't need arrays as long as these will
> be. Fixing those array sizes to be settable at runtime though is not a
> trivial project though.

Indeed. Hopefully the above is sufficient.

Thanks for the review!
Ryan

>
>>
>>>> /*
>>>> * The context of a single thread, including the request currently being
>>>> @@ -190,14 +192,14 @@ struct svc_rqst {
>>>> struct xdr_stream rq_res_stream;
>>>> struct page *rq_scratch_page;
>>>> struct xdr_buf rq_res;
>>>> - struct page *rq_pages[RPCSVC_MAXPAGES + 1];
>>>> + struct page *rq_pages[RPCSVC_MAXPAGES_MAX + 1];
>>>> struct page * *rq_respages; /* points into rq_pages */
>>>> struct page * *rq_next_page; /* next reply page to use */
>>>> struct page * *rq_page_end; /* one past the last page */
>>>>
>>>> struct folio_batch rq_fbatch;
>>>> - struct kvec rq_vec[RPCSVC_MAXPAGES]; /* generally useful.. */
>>>> - struct bio_vec rq_bvec[RPCSVC_MAXPAGES];
>>>> + struct kvec rq_vec[RPCSVC_MAXPAGES_MAX]; /* generally useful.. */
>>>> + struct bio_vec rq_bvec[RPCSVC_MAXPAGES_MAX];
>>>>
>>>> __be32 rq_xid; /* transmission id */
>>>> u32 rq_prog; /* program number */
>>>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>>>> index d33bab33099ab..7c6441e8d6f7a 100644
>>>> --- a/include/linux/sunrpc/svc_rdma.h
>>>> +++ b/include/linux/sunrpc/svc_rdma.h
>>>> @@ -200,7 +200,7 @@ struct svc_rdma_recv_ctxt {
>>>> struct svc_rdma_pcl rc_reply_pcl;
>>>>
>>>> unsigned int rc_page_count;
>>>> - struct page *rc_pages[RPCSVC_MAXPAGES];
>>>> + struct page *rc_pages[RPCSVC_MAXPAGES_MAX];
>>>> };
>>>>
>>>> /*
>>>> @@ -242,7 +242,7 @@ struct svc_rdma_send_ctxt {
>>>> void *sc_xprt_buf;
>>>> int sc_page_count;
>>>> int sc_cur_sge_no;
>>>> - struct page *sc_pages[RPCSVC_MAXPAGES];
>>>> + struct page *sc_pages[RPCSVC_MAXPAGES_MAX];
>>>> struct ib_sge sc_sges[];
>>>> };
>>>>
>>>> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
>>>> index 7c78ec6356b92..6c6bcc82685a3 100644
>>>> --- a/include/linux/sunrpc/svcsock.h
>>>> +++ b/include/linux/sunrpc/svcsock.h
>>>> @@ -40,7 +40,7 @@ struct svc_sock {
>>>>
>>>> struct completion sk_handshake_done;
>>>>
>>>> - struct page * sk_pages[RPCSVC_MAXPAGES]; /* received data */
>>>> + struct page * sk_pages[RPCSVC_MAXPAGES_MAX]; /* received data */
>>>> };
>>>>
>>>> static inline u32 svc_sock_reclen(struct svc_sock *svsk)
>>>
>>
>