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Thu, 20 Aug 2026 18:56:47 -0700 (PDT) From: Zhan Xusheng X-Google-Original-From: Zhan Xusheng To: Gao Xiang , Chao Yu Cc: Jingbo Xu , zhanxusheng@xiaomi.com, linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, Zhan Xusheng Subject: [PATCH v2] erofs: support splice() in inode_share mode Date: Fri, 21 Aug 2026 09:56:41 +0800 Message-ID: <20260821015641.1936276-1-zhanxusheng@xiaomi.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Zhan Xusheng From: Zhan Xusheng erofs_ishare_fops routes everything that touches the page cache to the backing file in ->private_data: read_iter clones the iocb onto it, mmap does vma_set_file(), fadvise calls vfs_fadvise() on it. splice_read was left as filemap_splice_read(), which works on the user file's own mapping: it does init_sync_kiocb(&iocb, in), and filemap_get_pages() then takes iocb->ki_filp->f_mapping. So splice() and sendfile() fill the per-inode page cache rather than the shared one. The content is the same either way, since erofs_fill_inode() sets a_ops on that mapping too, which is why this went unnoticed. Two identical 8 MiB files under inode_share, reading one of them with splice(2) alone, in pages: before own 2048 shared 0 after own 0 shared 2048 "own" is cachestat(fd), which reports the file's own mapping; "shared" is mmap()+mincore(), which erofs_ishare_mmap() redirects to the backing file. Read through the backing file, as read_iter already does. Link: https://lore.kernel.org/all/b7dc7192-d586-45a2-bc4a-b41dc681c9bb@linu= x.alibaba.com/ Signed-off-by: Zhan Xusheng Reviewed-by: Chao Yu Reviewed-by: Jingbo Xu \ --- v1->v2: - Retitled and dropped the Fixes tag: the sharing is best effort, so this is an enhancement rather than a fix. - Added the measured before/after. - Left file_accessed() alone, since it is a no-op under SB_NOATIME. - An erofs-utils test is sent separately against experimental-tests. v1: https://lore.kernel.org/all/20260820064441.1083470-1-zhanxusheng@xiaomi= .com fs/erofs/ishare.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c index fa7d4112dec5..01dc53e9e3ad 100644 --- a/fs/erofs/ishare.c +++ b/fs/erofs/ishare.c @@ -148,6 +148,13 @@ static int erofs_ishare_mmap(struct file *file, struct= vm_area_struct *vma) return generic_file_readonly_mmap(file, vma); } =20 +static ssize_t erofs_ishare_splice_read(struct file *in, loff_t *ppos, + struct pipe_inode_info *pipe, + size_t len, unsigned int flags) +{ + return filemap_splice_read(in->private_data, ppos, pipe, len, flags); +} + static int erofs_ishare_fadvise(struct file *file, loff_t offset, loff_t len, int advice) { @@ -161,7 +168,7 @@ const struct file_operations erofs_ishare_fops =3D { .mmap =3D erofs_ishare_mmap, .release =3D erofs_ishare_file_release, .get_unmapped_area =3D thp_get_unmapped_area, - .splice_read =3D filemap_splice_read, + .splice_read =3D erofs_ishare_splice_read, .fadvise =3D erofs_ishare_fadvise, }; =20 --=20 2.43.0