[Virtio-fs] [PATCH v7 6/7] fuse: mark inode DONT_CACHE when per inode DAX hint changes

[JeffleXu]

On 11/10/21 11:50 PM, Miklos Szeredi wrote:
> On Tue, 2 Nov 2021 at 06:26, Jeffle Xu <jefflexu at linux.alibaba.com> wrote:
>>
>> When the per inode DAX hint changes while the file is still *opened*, it
>> is quite complicated and maybe fragile to dynamically change the DAX
>> state.
>>
>> Hence mark the inode and corresponding dentries as DONE_CACHE once the
>> per inode DAX hint changes, so that the inode instance will be evicted
>> and freed as soon as possible once the file is closed and the last
>> reference to the inode is put. And then when the file gets reopened next
>> time, the new instantiated inode will reflect the new DAX state.
>>
>> In summary, when the per inode DAX hint changes for an *opened* file, the
>> DAX state of the file won't be updated until this file is closed and
>> reopened later.
> 
> This patch does nothing, since fuse already uses .drop_inode =
> generic_delete_inode, which is has the same effect as setting
> I_DONTCACHE, at least in the fuse case (inode should never be dirty at
> eviction).  

Yes, it is. .drop_inode() of FUSE will always free inode. Here we only
need to set dentry as DCACHE_DONTCACHE. Here I just call
d_mark_dontcache() directly, though I_DONTCACHE is useless but harmless
in the case of FUSE...


> In fact it may be cleaner to set I_DONTCACHE
> unconditionally and remove the .drop_inode callback setting.

It works in both cases, I mean, in current case (current code retained
untouched) and the case you described above.

-- 
Thanks,
Jeffle