On Thu, 2010-09-16 at 09:12 +0900, KAMEZAWA Hiroyuki wrote: > I hear a customer's case. His server generates 3-80000+ new dentries per day > and dentries will be piled up to 1000000+ in a month. This makes open()'s > performance very bad because Hash-lookup will be heavy. (He has very big memory.) > > What we could ask him was > - rewrite your application. or > - reboot once in a month (and change hash size) or > - drop_cache once in a month > > Because their servers cannot stop, he used drop_caches once in a month > while his server is idle, at night. Changing HashSize cannot be a permanent > fix because he may not stop the server for years. That is a really interesting case. They must have a *ton* of completely extra memory laying around. Do they not have much page cache activity? It usually balances out the dentry/inode caches. Would this user be better off with a smaller dentry hash in general? Is it special hardware that should _have_ a lower default hash size? > For rare users who have 10000000+ of files and tons of free memory, drop_cache > can be an emergency help. In this case, though, would a WARN_ON() in an emergency be such a bad thing? They evidently know what they're doing, and shouldn't be put off by it. -- Dave -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>