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From: Baoquan He To: Kairui Song Cc: linux-mm@kvack.org, akpm@linux-foundation.org, chrisl@kernel.org, usama.arif@linux.dev, baohua@kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, youngjun.park@lge.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 2/3] mm/swap: use swap_ops to register swap device's methods Message-ID: References: <20260512104201.716213-1-baoquan.he@linux.dev> <20260512104201.716213-3-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: rspam02 X-Rspamd-Queue-Id: E3705180004 X-Rspam-User: X-Stat-Signature: 5wmmpkwy1y54zjf9z87r58zti3fpww4s X-HE-Tag: 1778724378-687294 X-HE-Meta: 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 dpnt6BkM mF4dn96hH3LwDbqnw8jHnFvwpIXcHgAYM6FVVRX5/3Gr6yGCQScM+HEEB3WdFIAdFfXeNoBBVPz2MS3jEAo/gb9LVBz70N/gqt3BLDLkDk9VI1yW52Bk7zJ13fzc8hdOcvaGpBqdz0lL2OtC6SX9hSM9rVF2gqYmYI+yvh2fNMWJB3dUdRoANi+xR50bmhCnVw4F3KdOtfN/E7FJhkItx8NJ/h0rasf32OEnBUhO+wSx3S3sxNBvTbbpBLLs2ruGiKd8SqihxqkscTwaeIN59jDKgJRWC2ABrkRD87sjUwn9EK6gYxS4/CcXPpn4We73LuICJ0K1ga4hvG1VCcfnyZEQQvA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 05/13/26 at 01:53am, Kairui Song wrote: > On Tue, May 12, 2026 at 6:50 PM Baoquan He wrote: > > > > This simplifies codes and makes logic clearer. And also makes later any > > new swap device type being added easier to handle. > > > > Currently there are three types of swap devices: bdev_fs, bdev_sync > > and bdev_async, and only operations read_folio and write_folio are > > included. In the future, there could be more swap device types added > > and more appropriate opeations adapted into swap_ops. > > opeations -> operations Will fix, thanks. > > > > > Suggested-by: Chris Li > > Acked-by: Chris Li > > Co-developed-by: Barry Song > > Signed-off-by: Barry Song > > Signed-off-by: Baoquan He > > A few nitpicks below: > > > -void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug) > > -{ > > - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); > > - > > - VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio); > > This sanify check is dropped and not added back in anywhere. This is > fine, but it might be better to have a similar VM_WARN_ON_FOLIO in > swap_writeout? Good catch. In the old code, it's called by both swap_writeout() and zswap_writeback_entry(). In zswap_writeback_entry(), the folio is allocated in-place, we don't need to worry about it now. I am fine to add it back in swap_writeout() because adding it inside all three swap_write_xxx() is a little too much. Cscope tag: __swap_writepage # line filename / context / line 1 288 /home/bhe/code/linux/mm/page_io.c <> __swap_writepage(folio, swap_plug); 2 1053 /home/bhe/code/linux/mm/zswap.c <> __swap_writepage(folio, NULL); > > > void swap_read_folio(struct folio *folio, struct swap_iocb **plug) > > { > > struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); > > @@ -642,13 +664,7 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug) > > /* We have to read from slower devices. Increase zswap protection. */ > > zswap_folio_swapin(folio); > > > > - if (data_race(sis->flags & SWP_FS_OPS)) { > > - swap_read_folio_fs(folio, plug); > > - } else if (synchronous) { > > - swap_read_folio_bdev_sync(folio, sis); > > - } else { > > - swap_read_folio_bdev_async(folio, sis); > > - } > > + sis->ops->read_folio(sis, folio, plug); > > > > finish: > > if (workingset) { > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 4840fd40f36f..8c42632e6765 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -3780,6 +3780,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > > goto free_swap_zswap; > > } > > > > + /* > > + * init_swap_ops() sets si->ops based on flags. It does not need > > + * swapon_mutex, and must complete before enable_swap_info() > > + * exposes the device. > > + */ > > + error = init_swap_ops(si); > > + if (error) > > + goto bad_swap_unlock_inode; > > I checked the comment above previously and it looked good. But the > error label seems not that correct after double check. inode->i_flags > will keep the S_SWAPFILE flag. Maybe something like add a > inode->i_flags &= ~S_SWAPFILE here and goto free_swap_zswap. Sorry I > didn't check this part carefully last time. Right. How about moving it zswap_swapon() because it only relies on si->flags setting currently? > > But fortunately, init_swap_ops will never fail at this moment so the > issue never triggers. > > > + > > mutex_lock(&swapon_mutex); > > prio = DEF_SWAP_PRIO; > > if (swap_flags & SWAP_FLAG_PREFER) > > diff --git a/mm/zswap.c b/mm/zswap.c > > index 4b5149173b0e..192401f46de4 100644 > > --- a/mm/zswap.c > > +++ b/mm/zswap.c > > @@ -1054,7 +1054,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry, > > folio_set_reclaim(folio); > > > > /* start writeback */ > > - __swap_writepage(folio, NULL); > > + si->ops->write_folio(si, folio, NULL); > > > > out: > > if (ret && ret != -EEXIST) { > > -- > > 2.52.0 > > > > Rest looks good to me! >