Re: [PATCH 5/5] ceph: Fix write storm on fscrypted files

[Viacheslav Dubeyko]

On Tue, 2025-12-30 at 18:43 -0800, Sam Edwards wrote:
> CephFS stores file data across multiple RADOS objects. An object is the
> atomic unit of storage, so the writeback code must clean only folios
> that belong to the same object with each OSD request.
> 
> CephFS also supports RAID0-style striping of file contents: if enabled,
> each object stores multiple unbroken "stripe units" covering different
> portions of the file; if disabled, a "stripe unit" is simply the whole
> object. The stripe unit is (usually) reported as the inode's block size.
> 
> Though the writeback logic could, in principle, lock all dirty folios
> belonging to the same object, its current design is to lock only a
> single stripe unit at a time. Ever since this code was first written,
> it has determined this size by checking the inode's block size.
> However, the relatively-new fscrypt support needed to reduce the block
> size for encrypted inodes to the crypto block size (see 'fixes' commit),
> which causes an unnecessarily high number of write operations (~1024x as
> many, with 4MiB objects) and grossly degraded performance.

Do you have any benchmarking results that prove your point?

Thanks,
Slava.

> 
> Fix this (and clarify intent) by using i_layout.stripe_unit directly in
> ceph_define_write_size() so that encrypted inodes are written back with
> the same number of operations as if they were unencrypted.
> 
> Fixes: 94af0470924c ("ceph: add some fscrypt guardrails")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sam Edwards <CFSworks@xxxxxxxxx>
> ---
>  fs/ceph/addr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index b3569d44d510..cb1da8e27c2b 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -1000,7 +1000,8 @@ unsigned int ceph_define_write_size(struct address_space *mapping)
>  {
>  	struct inode *inode = mapping->host;
>  	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
> -	unsigned int wsize = i_blocksize(inode);
> +	struct ceph_inode_info *ci = ceph_inode(inode);
> +	unsigned int wsize = ci->i_layout.stripe_unit;
>  
>  	if (fsc->mount_options->wsize < wsize)
>  		wsize = fsc->mount_options->wsize;