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Subject: [PATCH 1/2] MM: handle THP in swap_*page_fs()
From:   NeilBrown <neilb@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Christoph Hellwig <hch@lst.de>,
        Miaohe Lin <linmiaohe@huawei.com>, linux-nfs@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Date:   Fri, 29 Apr 2022 10:43:34 +1000
Message-ID: <165119301488.15698.9457662928942765453.stgit@noble.brown>
In-Reply-To: <165119280115.15698.2629172320052218921.stgit@noble.brown>
References: <165119280115.15698.2629172320052218921.stgit@noble.brown>
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Pages passed to swap_readpage()/swap_writepage() are not necessarily all
the same size - there may be transparent-huge-pages involves.

The BIO paths of swap_*page() handle this correctly, but the SWP_FS_OPS
path does not.

So we need to use thp_size() to find the size, not just assume
PAGE_SIZE, and we need to track the total length of the request, not
just assume it is "page * PAGE_SIZE".

Reported-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: NeilBrown <neilb@suse.de>
---
 mm/page_io.c |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index c132511f521c..d636a3531cad 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -239,6 +239,7 @@ struct swap_iocb {
 	struct kiocb		iocb;
 	struct bio_vec		bvec[SWAP_CLUSTER_MAX];
 	int			pages;
+	int			len;
 };
 static mempool_t *sio_pool;
 
@@ -261,7 +262,7 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 	struct page *page = sio->bvec[0].bv_page;
 	int p;
 
-	if (ret != PAGE_SIZE * sio->pages) {
+	if (ret != sio->len) {
 		/*
 		 * In the case of swap-over-nfs, this can be a
 		 * temporary failure if the system has limited
@@ -301,7 +302,7 @@ static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
 		sio = *wbc->swap_plug;
 	if (sio) {
 		if (sio->iocb.ki_filp != swap_file ||
-		    sio->iocb.ki_pos + sio->pages * PAGE_SIZE != pos) {
+		    sio->iocb.ki_pos + sio->len != pos) {
 			swap_write_unplug(sio);
 			sio = NULL;
 		}
@@ -312,10 +313,12 @@ static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
 		sio->iocb.ki_complete = sio_write_complete;
 		sio->iocb.ki_pos = pos;
 		sio->pages = 0;
+		sio->len = 0;
 	}
 	sio->bvec[sio->pages].bv_page = page;
-	sio->bvec[sio->pages].bv_len = PAGE_SIZE;
+	sio->bvec[sio->pages].bv_len = thp_size(page);
 	sio->bvec[sio->pages].bv_offset = 0;
+	sio->len += thp_size(page);
 	sio->pages += 1;
 	if (sio->pages == ARRAY_SIZE(sio->bvec) || !wbc->swap_plug) {
 		swap_write_unplug(sio);
@@ -371,8 +374,7 @@ void swap_write_unplug(struct swap_iocb *sio)
 	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
 	int ret;
 
-	iov_iter_bvec(&from, WRITE, sio->bvec, sio->pages,
-		      PAGE_SIZE * sio->pages);
+	iov_iter_bvec(&from, WRITE, sio->bvec, sio->pages, sio->len);
 	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
 	if (ret != -EIOCBQUEUED)
 		sio_write_complete(&sio->iocb, ret);
@@ -383,7 +385,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
 	int p;
 
-	if (ret == PAGE_SIZE * sio->pages) {
+	if (ret == sio->len) {
 		for (p = 0; p < sio->pages; p++) {
 			struct page *page = sio->bvec[p].bv_page;
 
@@ -415,7 +417,7 @@ static void swap_readpage_fs(struct page *page,
 		sio = *plug;
 	if (sio) {
 		if (sio->iocb.ki_filp != sis->swap_file ||
-		    sio->iocb.ki_pos + sio->pages * PAGE_SIZE != pos) {
+		    sio->iocb.ki_pos + sio->len != pos) {
 			swap_read_unplug(sio);
 			sio = NULL;
 		}
@@ -426,10 +428,12 @@ static void swap_readpage_fs(struct page *page,
 		sio->iocb.ki_pos = pos;
 		sio->iocb.ki_complete = sio_read_complete;
 		sio->pages = 0;
+		sio->len = 0;
 	}
 	sio->bvec[sio->pages].bv_page = page;
-	sio->bvec[sio->pages].bv_len = PAGE_SIZE;
+	sio->bvec[sio->pages].bv_len = thp_size(page);
 	sio->bvec[sio->pages].bv_offset = 0;
+	sio->len += thp_size(page);
 	sio->pages += 1;
 	if (sio->pages == ARRAY_SIZE(sio->bvec) || !plug) {
 		swap_read_unplug(sio);
@@ -521,8 +525,7 @@ void __swap_read_unplug(struct swap_iocb *sio)
 	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
 	int ret;
 
-	iov_iter_bvec(&from, READ, sio->bvec, sio->pages,
-		      PAGE_SIZE * sio->pages);
+	iov_iter_bvec(&from, READ, sio->bvec, sio->pages, sio->len);
 	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
 	if (ret != -EIOCBQUEUED)
 		sio_read_complete(&sio->iocb, ret);