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Thunderbird Subject: Re: [PATCH 08/10] btrfs: keep the free space cache inode mapping at order 0 To: Tal Zussman , David Sterba , Chris Mason Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260906-btrfs-folio-conversions-v1-0-834b9d7b06f5@columbia.edu> <20260906-btrfs-folio-conversions-v1-8-834b9d7b06f5@columbia.edu> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCZxF1YAUJEP5a 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h9L5inTHfA02KEw+c0U34L0tA75wJ1SlwaIxO+JfKJ7pYnAeCp9Wy8vVEiQ5IZJ7qnSll+2Xm jHKJfrvOPt0ObcZG4oWon19bxBMbgaudSy5fVXdiv/Yki+OVi3ybtdzTjCEEFHOdDcxoX4VuX HYXbp+zaokf184zkXVz0HIfG4IbjgOXR5Ca8mlmPCeD4QZ52GRIbcs55XQTEGrzVnCkACWTT7 VjMXbjuDYgMY0/iZ5J9BV8qPp4+1fnavIdA4ytQPVT81grrHj5eiYcwt9umSs5SnB7VpfTuZq L+yP3KSfPuyVxhD1sdaf9wriEbcLZgvzn8uCpt5mSkKcXH2cZEbVXNjvwsJi+/sg2JRtqjnIQ w3CO9VnNMcD5ITjmwOJg8QO3YLDy0u4M6LELBRqYCW6+POCdD5WBPjkokf3MAuetfLzDO7EXt uYneBb07ahHsETxRPfnL6q =E5=9C=A8 2026/9/7 07:59, Tal Zussman =E5=86=99=E9=81=93: > The free space cache inode is a data inode, so the read path enables > large folios on its mapping. The v1 cache code assumes one page per > folio. With a large folio, consecutive __filemap_get_folio() calls in > io_ctl_prepare_pages() would return the same folio and deadlock on the > second FGP_LOCK. >=20 > The v1 on-disk format is PAGE_SIZE granular, so keep the mapping at > order 0 rather than teaching the io_ctl code about large folios. >=20 > Signed-off-by: Tal Zussman V1 space cache is already disabled by commit 545e560a5b0f ("btrfs:=20 disable v1 space cache"). I do not think you should add such check for things that we're already=20 planning to fully remove. > --- > fs/btrfs/btrfs_inode.h | 7 +++++++ > 1 file changed, 7 insertions(+) >=20 > diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h > index 89e5e9c0c904..5d85aa69db13 100644 > --- a/fs/btrfs/btrfs_inode.h > +++ b/fs/btrfs/btrfs_inode.h > @@ -502,6 +502,13 @@ static inline void btrfs_set_inode_mapping_order(st= ruct btrfs_inode *inode) > /* Metadata inode should not reach here. */ > ASSERT(is_data_inode(inode)); > =20 > + /* > + * The v1 free space cache operates on PAGE_SIZE chunks and assumes > + * one page per folio. Leave it at order 0. > + */ > + if (btrfs_is_free_space_inode(inode)) > + return; > + > mapping_set_folio_order_range(inode->vfs_inode.i_mapping, > inode->root->fs_info->block_min_order, > inode->root->fs_info->block_max_order); >=20