Re: [RFC PATCH v2] fuse: add new function to invalidate cache for all inodes

[Bernd Schubert <bernd@bsbernd.com>]

On 2/10/25 11:48, Luis Henriques wrote:
> [re-sending -- for some reason I did a simple 'reply', not a 'reply-all'.]
> 
> On Mon, Feb 10 2025, Bernd Schubert wrote:
> 
>> On 2/10/25 10:48, Luis Henriques wrote:
>>> Currently userspace is able to notify the kernel to invalidate the cache for
>>> an inode.  This means that, if all the inodes in a filesystem need to be
>>> invalidated, then userspace needs to iterate through all of them and do this
>>> kernel notification separately.
>>>
>>> This patch adds a new option that allows userspace to invalidate all the
>>> inodes with a single notification operation.  In addition to invalidate all
>>> the inodes, it also shrinks the sb dcache.
>>>
>>> Signed-off-by: Luis Henriques <luis@igalia.com>
>>> ---
>>> Hi!
>>>
>>> As suggested by Bernd, this patch v2 simply adds an helper function that
>>> will make it easier to replace most of it's code by a call to function
>>> super_iter_inodes() when Dave Chinner's patch[1] eventually gets merged.
>>>
>>> [1] https://lore.kernel.org/r/20241002014017.3801899-3-david@fromorbit.com
>>>
>>>  fs/fuse/inode.c           | 59 +++++++++++++++++++++++++++++++++++++++
>>>  include/uapi/linux/fuse.h |  3 ++
>>>  2 files changed, 62 insertions(+)
>>>
>>> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
>>> index e9db2cb8c150..be51b53006d8 100644
>>> --- a/fs/fuse/inode.c
>>> +++ b/fs/fuse/inode.c
>>> @@ -547,6 +547,62 @@ struct inode *fuse_ilookup(struct fuse_conn *fc, u64 nodeid,
>>>  	return NULL;
>>>  }
>>>  
>>> +static void inval_single_inode(struct inode *inode, struct fuse_conn *fc)
>>> +{
>>> +	struct fuse_inode *fi;
>>> +
>>> +	fi = get_fuse_inode(inode);
>>> +	spin_lock(&fi->lock);
>>> +	fi->attr_version = atomic64_inc_return(&fc->attr_version);
>>> +	spin_unlock(&fi->lock);
>>> +	fuse_invalidate_attr(inode);
>>> +	forget_all_cached_acls(inode);
>>
>>
>> Thank you, much easier to read.
>>
>> Could fuse_reverse_inval_inode() call into this?
> 
> Yep, it could indeed.  I'll do that in the next iteration, thanks!
> 
>> What are the semantics 
>> for  invalidate_inode_pages2_range() in this case? Totally invalidate?
>> No page cache invalidation at all as right now? If so, why?
> 
> So, if I change fuse_reverse_inval_inode() to use this help, it will still
> need to keep the call to invalidate_inode_pages2_range().  But in the new
> function fuse_reverse_inval_all(), I'm not doing it explicitly.  Instead,
> that function calls into shrink_dcache_sb().  I *think* that by doing so
> the invalidation will eventually happen.  Or am I wrong assuming that?

I think it will drop it, if the dentry cache is the last user/reference
of the inode. My issue is that it changes semantics a bit - without
FUSE_INVAL_ALL_INODES the page cache is invalidated based on the given
offset. Obviously we cannot give the offset for all inodes, but we
at least document the different semantics in a comment above
FUSE_INVAL_ALL_INODES? Sorry, should have asked earlier for it, just
busy with multiple things in parallel...


Thanks,
Bernd