On 03/06/11 10:43, Vasily Novikov wrote:
> Hi Eric,
>
> We are moving to fanotify at the moment. It meets our needs except
> couple minor issues we would like to be fixed in future versions:
>
> 1. The file is thrown out of the cache only when it is modified. But in
> case there are different scan options for different dirs that's not
> enough. So we also need it to be evicted from cache on rename or number
> of hard links change.
> It is the most important issue for us.
> The patch is in attachment: add_clear_cache_events.patch
This is interesting, as it makes the cache less efficient for those
users who don't have different scanning within a filesystem.
Our only equivalent things are exclusions, which we handle by not
marking the responses for exclusions as cache-able.
>
> 2. We can't use unlimited cache because it can potentially grab too much
> memory and slow down a system. In case we use limited cache it can be
> easily filled with not very frequently used files. So the only option we
> have at the moment is to clear cache every time it is full.
> The solution we consider the most appropriate is to introduce
> replaceable marks and LRU cache for them in fanotify.
> So we suggest to introduce a new flag FAN_MARK_REPLACEABLE for marks.
> That will not break the current API.
> The patch is in attachment: marks_lru_cache.patch
IIRC the cache is stored in the inodes themselves, so will automatically
be culled as inodes are pushed out of memory?
>
> 3. The fanotify file descriptor is always ready to be written to it. But
> it's poll method says the opposite. In case you handle it by yourself
> that's not a problem. But in case you use some async io library as we do
> that polls fds internally it doesn't work.
> The patch is in attachment: fanotify_write_poll.patch
>
This seems like a good fix.
--
Douglas Leeder, Senior Software Engineer
Sophos Limited, The Pentagon, Abingdon Science Park, Abingdon, OX14 3YP, United Kingdom.
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