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Message-ID: <CAHbLzko+9nBem8GnxQJ8RQu7bizQMMmS1TNqbRXcgkjUs+JuMw@mail.gmail.com>
Date: Fri, 29 Apr 2022 12:04:41 -0700
From: Yang Shi <shy828301@...il.com>
To: NeilBrown <neilb@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Christoph Hellwig <hch@....de>,
Miaohe Lin <linmiaohe@...wei.com>, linux-nfs@...r.kernel.org,
Linux MM <linux-mm@...ck.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] MM: handle THP in swap_*page_fs()
On Thu, Apr 28, 2022 at 5:44 PM NeilBrown <neilb@...e.de> wrote:
>
> 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".
Swap-over-nfs doesn't support THP swap IIUC. So SWP_FS_OPS should not
see THP at all. But I agree to remove the assumption about page size
in this path.
>
> Reported-by: Miaohe Lin <linmiaohe@...wei.com>
> Signed-off-by: NeilBrown <neilb@...e.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);
>
>
>
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