On Tue, 31 May 2011, Chris Mason wrote: > Excerpts from Hugh Dickins's message of 2011-05-31 13:05:27 -0400: > > On Tue, 31 May 2011, Dan Magenheimer wrote: > > > > > > > > truncate_inode_pages_range() and invalidate_inode_pages2_range() > > > > call cleancache_flush_inode(mapping) before and after: shouldn't > > > > invalidate_mapping_pages() be doing the same? > > > > > > I don't claim to be an expert on VFS, and so I have cc'ed > > > Chris Mason who originally placed the cleancache hooks > > > in VFS, but I think this patch is unnecessary. Instead > > > of flushing ALL of the cleancache pages belonging to > > > the inode with cleancache_flush_inode, the existing code > > > eventually calls __delete_from_page_cache on EACH page > > > that is being invalidated. > > > > On each one that's in pagecache (and satisfies the other "can we > > do it easily?" conditions peculiar to invalidate_mapping_pages()). > > But there may be other slots in the range that don't reach > > __delete_from_page_cache() e.g. because not currently in pagecache, > > but whose cleancache ought to be flushed. I think that's what a > > caller of invalidate_mapping_pages(), e.g. drop caches, expects. > > We call invalidate_mapping_pages from prune_icache, so if we drop the > cleancache there we lose the cache entries any time the inode is dropped > from ram. I hadn't noticed that use of invalidate_mapping_pages(). Right, I can understand that you wouldn't want to drop the cleancache there. I was more conscious of the dispose_list() at the end of prune_icache(), which would call truncate_inode_pages(), which would flush cleancache. Ah, but inode only gets on the freeable list if can_unuse(inode), and one of the reasons to retain the inode is if nrpages is non-0. All rather odd, and what it adds up to, I think, is that if that invalidate_mapping_pages() succeeds in removing all the pages from the page cache (but leaving some in cleancache), then the inode may advance to truncate_inode_pages(), and meet cleancache_flush_inode() there. (It happens to be called before the mapping->nrpages test.) All rather odd, both the pruning decisions and the cleancache decisions. > > Is there a specific case you're thinking of where we want to drop the > cleancache but don't have the pages? The case I was thinking of, where I'd met invalidate_mapping_pages() before, is fs/drop_caches.c ... which is about, er, dropping caches. (But in general, why would you care to keep the cleancache when you do have the pages? I thought its use was for the pages we don't have.) > > O_DIRECT perhaps? Hadn't given it a thought. But now you mention it, yes, that one looks like a worry too. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>