Hello, maybe the name of this topic could be "How hard should be life of filesystems?" but that's kind of broad topic and suggests too much of bikeshedding. I'd like to concentrate on concrete possible pain points between filesystems & VFS (possibly writeback or even generally MM). Lately, I've myself came across the two issues in $SUBJECT: 1) dropping of last file reference can happen from munmap() and in that case mmap_sem will be held when ->release() is called. Even more it could be held when ->evict_inode() is called to delete inode because inode was unlinked. 2) since flusher thread takes inode reference when writing inode out, the last inode reference can be dropped from flusher thread. Thus inode may get deleted in the flusher thread context. This does not seem that problematic on its own but if we realize progress of memory reclaim depends (at least from a longterm perspective) on flusher thread making progress, things start looking a bit uncertain. Even more so when we would like avoid ->writepage() calls from reclaim and let flusher thread do the work instead. That would then require filesystems to carefully design their ->evict_inode() routines so that things are not deadlockable. Both these issues should be avoidable (we can postpone fput() after we drop mmap_sem; we can tweak inode refcounting to avoid last iput() from flusher thread) but obviously there's some cost in the complexity of generic layer. So the question is, is it worth it? Certainly we can also discuss other pain points if people come with them. We should have enough know-how in place to be able to tell which changes are reasonably possible and which are not... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
