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Message-ID: <20240104114958.f3cit5q7syp3tn3a@quack3> Date: Thu, 4 Jan 2024 12:49:58 +0100 From: Jan Kara <jack@...e.cz> To: Matthew Wilcox <willy@...radead.org> Cc: Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk, roger.pau@...rix.com, colyli@...e.de, kent.overstreet@...il.com, joern@...ybastard.org, miquel.raynal@...tlin.com, richard@....at, vigneshr@...com, sth@...ux.ibm.com, hoeppner@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com, jejb@...ux.ibm.com, martin.petersen@...cle.com, clm@...com, josef@...icpanda.com, dsterba@...e.com, viro@...iv.linux.org.uk, brauner@...nel.org, nico@...xnic.net, xiang@...nel.org, chao@...nel.org, tytso@....edu, adilger.kernel@...ger.ca, jack@...e.com, konishi.ryusuke@...il.com, akpm@...ux-foundation.org, hare@...e.de, p.raghav@...sung.com, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org, linux-bcache@...r.kernel.org, linux-mtd@...ts.infradead.org, linux-s390@...r.kernel.org, linux-scsi@...r.kernel.org, linux-bcachefs@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org, linux-nilfs@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com Subject: Re: [PATCH RFC v3 for-6.8/block 09/17] btrfs: use bdev apis On Sat 23-12-23 17:31:55, Matthew Wilcox wrote: > On Thu, Dec 21, 2023 at 04:57:04PM +0800, Yu Kuai wrote: > > @@ -3674,16 +3670,17 @@ struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev, > > * Drop the page of the primary superblock, so later read will > > * always read from the device. > > */ > > - invalidate_inode_pages2_range(mapping, > > - bytenr >> PAGE_SHIFT, > > + invalidate_bdev_range(bdev, bytenr >> PAGE_SHIFT, > > (bytenr + BTRFS_SUPER_INFO_SIZE) >> PAGE_SHIFT); > > } > > > > - page = read_cache_page_gfp(mapping, bytenr >> PAGE_SHIFT, GFP_NOFS); > > - if (IS_ERR(page)) > > - return ERR_CAST(page); > > + nofs_flag = memalloc_nofs_save(); > > + folio = bdev_read_folio(bdev, bytenr); > > + memalloc_nofs_restore(nofs_flag); > > This is the wrong way to use memalloc_nofs_save/restore. They should be > used at the point that the filesystem takes/releases whatever lock is > also used during reclaim. I don't know btrfs well enough to suggest > what lock is missing these annotations. In principle I agree with you but in this particular case I agree the ask is just too big. I suspect it is one of btrfs btree locks or maybe chunk_mutex but I doubt even btrfs developers know and maybe it is just a cargo cult. And it is not like this would be the first occurence of this anti-pattern in btrfs - see e.g. device_list_add(), add_missing_dev(), btrfs_destroy_delalloc_inodes() (here the wrapping around invalidate_inode_pages2() looks really weird), and many others... Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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