From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 2 Oct 2000 18:52:59 -0300 (BRST) From: Rik van Riel Subject: Re: [highmem bug report against -test5 and -test6] Re: [PATCH] Re: simple FS application that hangs 2.4-test5, mem mgmt problem or FS buffer cache mgmt problem? (fwd) In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Ingo Molnar Cc: Linus Torvalds , Andrea Arcangeli , MM mailing list , "Stephen C. Tweedie" List-ID: On Mon, 2 Oct 2000, Ingo Molnar wrote: > yep, this would be nice, but i think it will be quite tough to > balance this properly. There are two kinds of bhs in this aging > scheme: 'normal' bhs (metadata), and 'virtual' bhs (aliased to a > page). Freeing a 'normal' bh will get rid of the bh, and will > (statistically) free the data buffer behind. A 'virtual' bh on > the other hand has only sizeof(*bh) bytes worth of RAM > footprint. This is easy. Normal page aging will take care of the buffermem pages. Freeing the buffer heads on pagecache pages is the only thing we need to do in refill_inactive_scan. > another thing is the complexity of marking a page dirty - right > now we can assume that page->buffers holds all the blocks. With > aging we must check wether a bh is there or not, The code must already be able to handle this. This is nothing new. > Plus some sort of locking has to be added as well - right now we > dont have to care about anyone else accessing page->buffers if > the PG_lock held - with an aging mechanizm this could get > tougher. OK, so we'll have: if (page->buffers && page->mapping && !TryLockPage(page)) { try_to_free_buffers(page); UnlockPage(page); } > > So if we have "lots" of memory, we basically optimize for speed (leave > > the cached mapping around), while if we get low on memory we > > automatically optimize for space (get rid of bh's when we don't know > > that we'll need them). > > i'd love to have all the cached objects within the system on a > global, size-neutral LRU list. (or at least attach a > last-accessed timestamp to them.) This way we could synchronize > the pagecache, inode/dentry and buffer-cache LRU lists. s/LRU/page aging/ ;) regards, Rik -- "What you're running that piece of shit Gnome?!?!" -- Miguel de Icaza, UKUUG 2000 http://www.conectiva.com/ http://www.surriel.com/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux.eu.org/Linux-MM/