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From: Baoquan He To: Barry Song Cc: linux-mm@kvack.org, akpm@linux-foundation.org, chrisl@kernel.org, usama.arif@linux.dev, kasong@tencent.com, nphamcs@gmail.com, shikemeng@huaweicloud.com, youngjun.park@lge.com, hch@infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 3/3] mm/swap: add unplug callback to swap_ops to fix leaky abstraction Message-ID: References: <20260515015737.890994-1-baoquan.he@linux.dev> <20260515015737.890994-4-baoquan.he@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A8CBC80002 X-Stat-Signature: hqr36eefrxwiztnfaw5z4dfx9dknd9jg X-Rspam-User: X-HE-Tag: 1778823807-59953 X-HE-Meta: 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 i6s7MCmP eN4zz3P5/MDIUEUktFgX+ru/Iv2KiL8M+8hwzPF63ugSfea7cpGtV/2NOk4ojl0kPO9KeJbUXnZ3qPgrcXM/YIxm9ZXCyWab1ps+m25Nzdc7NRjPtOcBCay54ZKmoYDk9UKg0l1V9YM4RImi0sPcmHrJOKFPPtqe4r41m3YY/XKgtijIO67Gah7eRcxzteI4K8p2GVPtgMR+O9jcuj26ulrE3Au2w8201scZppL298vXv/HfKp141SIXzKRA1BjakD9tzM1sHZA03VGHpZW5c+YR+xqm+KH7+CC2MIm458vN5rMNAwTVM4/anrYabe/80a/Lo Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 05/15/26 at 12:39pm, Barry Song wrote: > On Fri, May 15, 2026 at 9:58 AM Baoquan He wrote: > > > > When swap_ops was introduced, the FS-swap batch submission remained > > as a standalone swap_write_unplug() that directly called > > mapping->a_ops->swap_rw(). This meant callers still had implicit > > knowledge of filesystem internals rather than going through the > > swap_ops abstraction. > > > > Fix this by adding an unplug callback to struct swap_ops. > > Each ops table provides its own implementation: > > - bdev_fs_swap_ops uses the existing FS batch-submission logic > > - bdev_sync/bdev_async_swap_ops leave it NULL since block-layer > > plugging handles their I/O > > > > The swap_iocb now carries a pointer to its ops table so that > > swap_write_unplug() can dispatch through the callback without > > the caller needing to know the swap device type. > > > > Signed-off-by: Baoquan He > > --- > > mm/page_io.c | 11 ++++++++++- > > mm/swap.h | 1 + > > 2 files changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/mm/page_io.c b/mm/page_io.c > > index 38b94c560c37..2c36d261ad98 100644 > > --- a/mm/page_io.c > > +++ b/mm/page_io.c > > @@ -329,6 +329,7 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio) > > > > struct swap_iocb { > > struct kiocb iocb; > > + const struct swap_ops *ops; > > struct bio_vec bvec[SWAP_CLUSTER_MAX]; > > int pages; > > int len; > > @@ -401,6 +402,7 @@ static void swap_fs_write_folio(struct swap_info_struct *sis, > > init_sync_kiocb(&sio->iocb, swap_file); > > sio->iocb.ki_complete = sio_write_complete; > > sio->iocb.ki_pos = pos; > > + sio->ops = sis->ops; > > sio->pages = 0; > > sio->len = 0; > > } > > @@ -454,7 +456,7 @@ static void swap_bdev_async_write_folio(struct swap_info_struct *sis, > > submit_bio(bio); > > } > > > > -void swap_write_unplug(struct swap_iocb *sio) > > +static void swap_fs_write_folio_unplug(struct swap_iocb *sio) > > { > > struct iov_iter from; > > struct address_space *mapping = sio->iocb.ki_filp->f_mapping; > > @@ -466,6 +468,12 @@ void swap_write_unplug(struct swap_iocb *sio) > > sio_write_complete(&sio->iocb, ret); > > } > > > > +void swap_write_unplug(struct swap_iocb *sio) > > +{ > > + if (sio->ops && sio->ops->unplug) > > + sio->ops->unplug(sio); > > +} > > + > > Hi Baoquan, > > we have already "sis->ops" check in init_swap_ops, do we need !sis->ops > again? That's a good point, and no, I dont' think we need it. I will fix it in v8. Thanks. > > +int init_swap_ops(struct swap_info_struct *sis) > +{ > + ... > + > + if (!sis->ops || !sis->ops->read_folio || !sis->ops->write_folio) > + return -EINVAL; > + > + return 0; > +}