linux-kernel - Re: [PATCH V2] RDMA/siw: Convert siw_tx_hdt() to kmap_local

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Date:   Wed, 23 Jun 2021 08:34:37 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Bernard Metzler <BMT@...ich.ibm.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Doug Ledford <dledford@...hat.com>,
        Faisal Latif <faisal.latif@...el.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Kamal Heib <kheib@...hat.com>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] RDMA/siw: Convert siw_tx_hdt() to kmap_local_page()

On Wed, Jun 23, 2021 at 02:36:45PM +0000, Bernard Metzler wrote:
> -----ira.weiny@...el.com wrote: -----
> 
> >@@ -506,11 +513,12 @@ static int siw_tx_hdt(struct siw_iwarp_tx
> >*c_tx, struct socket *s)
> > 				page_array[seg] = p;
> > 
> > 				if (!c_tx->use_sendpage) {
> >-					iov[seg].iov_base = kmap(p) + fp_off;
> >-					iov[seg].iov_len = plen;
> >+					void *kaddr = kmap_local_page(page_array[seg]);
> 
> we can use 'kmap_local_page(p)' here

Yes but I actually did this on purpose as it makes the code read clearly that
the mapping is 'seg' element of the array.  Do you prefer 'p' because this is a
performant path?

> > 
> > 					/* Remember for later kunmap() */
> > 					kmap_mask |= BIT(seg);
> >+					iov[seg].iov_base = kaddr + fp_off;
> >+					iov[seg].iov_len = plen;
> > 
> > 					if (do_crc)
> > 						crypto_shash_update(
> >@@ -518,7 +526,7 @@ static int siw_tx_hdt(struct siw_iwarp_tx *c_tx,
> >struct socket *s)
> > 							iov[seg].iov_base,
> > 							plen);
> 
> This patch does not apply for me. Would I have to install first
> your [Patch 3/4] -- since the current patch references kmap_local_page()
> already? Maybe it is better to apply if it would be just one siw
> related patch in that series?

Yes the other patch goes first.  I split it out to make this more difficult
change more reviewable.  I could squash them as it is probably straight forward
enough but I've been careful with this in other subsystems.

Jason, do you have any issue with squashing the 2 patches?

> 
> 
> 
> > 				} else if (do_crc) {
> >-					kaddr = kmap_local_page(p);
> >+					kaddr = kmap_local_page(page_array[seg]);
> 
> using 'kmap_local_page(p)' as you had it is straightforward
> and I would prefer it.

OK.  I think this reads cleaner but I can see 'p' being more performant.

> 
> > 					crypto_shash_update(c_tx->mpa_crc_hd,
> > 							    kaddr + fp_off,
> > 							    plen);
> >@@ -542,7 +550,7 @@ static int siw_tx_hdt(struct siw_iwarp_tx *c_tx,
> >struct socket *s)
> > 
> > 			if (++seg > (int)MAX_ARRAY) {
> > 				siw_dbg_qp(tx_qp(c_tx), "to many fragments\n");
> >-				siw_unmap_pages(page_array, kmap_mask);
> >+				siw_unmap_pages(iov, kmap_mask, MAX_ARRAY);
> 
> to minimize the iterations over the byte array in 'siw_unmap_pages()',
> we may pass seg-1 instead of MAX_ARRAY

Sounds good.

> 
> 
> > 				wqe->processed -= c_tx->bytes_unsent;
> > 				rv = -EMSGSIZE;
> > 				goto done_crc;
> >@@ -593,7 +601,7 @@ static int siw_tx_hdt(struct siw_iwarp_tx *c_tx,
> >struct socket *s)
> > 	} else {
> > 		rv = kernel_sendmsg(s, &msg, iov, seg + 1,
> > 				    hdr_len + data_len + trl_len);
> >-		siw_unmap_pages(page_array, kmap_mask);
> >+		siw_unmap_pages(iov, kmap_mask, MAX_ARRAY);
> 
> to minimize the iterations over the byte array in 'siw_unmap_pages()',
> we may pass seg instead of MAX_ARRAY

Will do.

Thanks for the review!  :-D
Ira