[PATCH v4 1/2] mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()

[PATCH v4 1/2] mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()

[David Carlier]

sio_read_complete() uses sio->pages to account global PSWPIN vm events,
but sio->pages tracks the number of bvec entries (folios), not base
pages.

While large folios cannot currently reach this path (SWP_FS_OPS and
SWP_SYNCHRONOUS_IO are mutually exclusive, and mTHP swap-in allocation
is gated on SWP_SYNCHRONOUS_IO), the accounting is semantically
inconsistent with the per-memcg path which correctly uses
folio_nr_pages().

Use sio->len >> PAGE_SHIFT instead, which gives the correct base page
count since sio->len is accumulated via folio_size(folio).

Signed-off-by: David Carlier <devnexen@gmail.com>
---
 mm/page_io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index 63b262f4c5a9..1389cd57ca88 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -497,7 +497,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 			folio_mark_uptodate(folio);
 			folio_unlock(folio);
 		}
-		count_vm_events(PSWPIN, sio->pages);
+		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
 	} else {
 		for (p = 0; p < sio->pages; p++) {
 			struct folio *folio = page_folio(sio->bvec[p].bv_page);
-- 
2.53.0

[PATCH v4 2/2] mm/page_io: rename swap_iocb->pages to swap_iocb->bvecs

[David Carlier]

swap_iocb->pages tracks the number of bvec entries (folios), not base
pages. Rename it to bvecs to accurately reflect its purpose.

Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Carlier <devnexen@gmail.com>
---
 mm/page_io.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index 1389cd57ca88..e524cb821d04 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -327,7 +327,7 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
 struct swap_iocb {
 	struct kiocb		iocb;
 	struct bio_vec		bvec[SWAP_CLUSTER_MAX];
-	int			pages;
+	int			bvecs;
 	int			len;
 };
 static mempool_t *sio_pool;
@@ -362,14 +362,14 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 		 */
 		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
 				   ret, swap_dev_pos(page_swap_entry(page)));
-		for (p = 0; p < sio->pages; p++) {
+		for (p = 0; p < sio->bvecs; p++) {
 			page = sio->bvec[p].bv_page;
 			set_page_dirty(page);
 			ClearPageReclaim(page);
 		}
 	}
 
-	for (p = 0; p < sio->pages; p++)
+	for (p = 0; p < sio->bvecs; p++)
 		end_page_writeback(sio->bvec[p].bv_page);
 
 	mempool_free(sio, sio_pool);
@@ -397,13 +397,13 @@ static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
 		init_sync_kiocb(&sio->iocb, swap_file);
 		sio->iocb.ki_complete = sio_write_complete;
 		sio->iocb.ki_pos = pos;
-		sio->pages = 0;
+		sio->bvecs = 0;
 		sio->len = 0;
 	}
-	bvec_set_folio(&sio->bvec[sio->pages], folio, folio_size(folio), 0);
+	bvec_set_folio(&sio->bvec[sio->bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
-	sio->pages += 1;
-	if (sio->pages == ARRAY_SIZE(sio->bvec) || !swap_plug) {
+	sio->bvecs += 1;
+	if (sio->bvecs == ARRAY_SIZE(sio->bvec) || !swap_plug) {
 		swap_write_unplug(sio);
 		sio = NULL;
 	}
@@ -477,7 +477,7 @@ void swap_write_unplug(struct swap_iocb *sio)
 	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
 	int ret;
 
-	iov_iter_bvec(&from, ITER_SOURCE, sio->bvec, sio->pages, sio->len);
+	iov_iter_bvec(&from, ITER_SOURCE, sio->bvec, sio->bvecs, sio->len);
 	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
 	if (ret != -EIOCBQUEUED)
 		sio_write_complete(&sio->iocb, ret);
@@ -489,7 +489,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 	int p;
 
 	if (ret == sio->len) {
-		for (p = 0; p < sio->pages; p++) {
+		for (p = 0; p < sio->bvecs; p++) {
 			struct folio *folio = page_folio(sio->bvec[p].bv_page);
 
 			count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
@@ -499,7 +499,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 		}
 		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
 	} else {
-		for (p = 0; p < sio->pages; p++) {
+		for (p = 0; p < sio->bvecs; p++) {
 			struct folio *folio = page_folio(sio->bvec[p].bv_page);
 
 			folio_unlock(folio);
@@ -559,13 +559,13 @@ static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
 		init_sync_kiocb(&sio->iocb, sis->swap_file);
 		sio->iocb.ki_pos = pos;
 		sio->iocb.ki_complete = sio_read_complete;
-		sio->pages = 0;
+		sio->bvecs = 0;
 		sio->len = 0;
 	}
-	bvec_set_folio(&sio->bvec[sio->pages], folio, folio_size(folio), 0);
+	bvec_set_folio(&sio->bvec[sio->bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
-	sio->pages += 1;
-	if (sio->pages == ARRAY_SIZE(sio->bvec) || !plug) {
+	sio->bvecs += 1;
+	if (sio->bvecs == ARRAY_SIZE(sio->bvec) || !plug) {
 		swap_read_unplug(sio);
 		sio = NULL;
 	}
@@ -666,7 +666,7 @@ void __swap_read_unplug(struct swap_iocb *sio)
 	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
 	int ret;
 
-	iov_iter_bvec(&from, ITER_DEST, sio->bvec, sio->pages, sio->len);
+	iov_iter_bvec(&from, ITER_DEST, sio->bvec, sio->bvecs, sio->len);
 	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
 	if (ret != -EIOCBQUEUED)
 		sio_read_complete(&sio->iocb, ret);
-- 
2.53.0

Re: [PATCH v4 2/2] mm/page_io: rename swap_iocb->pages to swap_iocb->bvecs

[David Hildenbrand (Arm)]

On 4/2/26 08:14, David Carlier wrote:
> swap_iocb->pages tracks the number of bvec entries (folios), not base
> pages. Rename it to bvecs to accurately reflect its purpose.
> 
> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
>  mm/page_io.c | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/page_io.c b/mm/page_io.c
> index 1389cd57ca88..e524cb821d04 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -327,7 +327,7 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
>  struct swap_iocb {
>  	struct kiocb		iocb;
>  	struct bio_vec		bvec[SWAP_CLUSTER_MAX];
> -	int			pages;
> +	int			bvecs;

bvec (an array of bvecs) vs bvecs. Hm.

Wouldn't it be cleaner to have

	struct bio_vec		bvecs[SWAP_CLUSTER_MAX];
	int			nr_bvecs;

?

-- 
Cheers,

David

Re: [PATCH v4 2/2] mm/page_io: rename swap_iocb->pages to swap_iocb->bvecs

[David CARLIER]

I went for it initially but I thought I saw bvecs in a message :) but
I do not mind it is just naming after all, let s go for it.

On Thu, 2 Apr 2026 at 08:15, David Hildenbrand (Arm) <david@kernel.org> wrote:
>
> On 4/2/26 08:14, David Carlier wrote:
> > swap_iocb->pages tracks the number of bvec entries (folios), not base
> > pages. Rename it to bvecs to accurately reflect its purpose.
> >
> > Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Signed-off-by: David Carlier <devnexen@gmail.com>
> > ---
> >  mm/page_io.c | 30 +++++++++++++++---------------
> >  1 file changed, 15 insertions(+), 15 deletions(-)
> >
> > diff --git a/mm/page_io.c b/mm/page_io.c
> > index 1389cd57ca88..e524cb821d04 100644
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> > @@ -327,7 +327,7 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
> >  struct swap_iocb {
> >       struct kiocb            iocb;
> >       struct bio_vec          bvec[SWAP_CLUSTER_MAX];
> > -     int                     pages;
> > +     int                     bvecs;
>
> bvec (an array of bvecs) vs bvecs. Hm.
>
> Wouldn't it be cleaner to have
>
>         struct bio_vec          bvecs[SWAP_CLUSTER_MAX];
>         int                     nr_bvecs;
>
> ?
>
> --
> Cheers,
>
> David

Re: [PATCH v4 1/2] mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()

[David Hildenbrand (Arm)]

On 4/2/26 08:14, David Carlier wrote:
> sio_read_complete() uses sio->pages to account global PSWPIN vm events,
> but sio->pages tracks the number of bvec entries (folios), not base
> pages.
> 
> While large folios cannot currently reach this path (SWP_FS_OPS and
> SWP_SYNCHRONOUS_IO are mutually exclusive, and mTHP swap-in allocation
> is gated on SWP_SYNCHRONOUS_IO), the accounting is semantically
> inconsistent with the per-memcg path which correctly uses
> folio_nr_pages().
> 
> Use sio->len >> PAGE_SHIFT instead, which gives the correct base page
> count since sio->len is accumulated via folio_size(folio).
> 
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David