From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4113218F.5050803@yahoo.com.au> Date: Fri, 06 Aug 2004 16:13:35 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH] 3/4: writeout watermarks References: <41130FB1.5020001@yahoo.com.au> <41130FD2.5070608@yahoo.com.au> <41131105.8040108@yahoo.com.au> <20040805222733.477b3017.akpm@osdl.org> <41131862.5050000@yahoo.com.au> <20040805224920.6755198d.akpm@osdl.org> In-Reply-To: <20040805224920.6755198d.akpm@osdl.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org List-ID: Andrew Morton wrote: > Nick Piggin wrote: > >>No, it is not that code I am worried about, you're actually doing >> this too (disregarding the admin's wishes): >> >> dirty_ratio = vm_dirty_ratio; >> if (dirty_ratio > unmapped_ratio / 2) >> dirty_ratio = unmapped_ratio / 2; >> >> if (dirty_ratio < 5) >> dirty_ratio = 5; >> > > > hm, OK, that's some "try to avoid writeback off the LRU" stuff. > Yep > But you said "This ensures we should always attempt to start background > writeout before synchronous writeout.". Does not the current code do that? > Basically what the above code, is scale the dirty_ratio with the amount of unmapped pages, however it doesn't also scale the dirty_background_ratio (it does after my patch). So it isn't difficult to imagine this causing dirty_ratio to become very close to dirty_background_ratio. The crude check prevents the values from becoming exactly equal. if (background_ratio >= dirty_ratio) background_ratio = dirty_ratio / 2; > >> So if the admin wants a dirty_ratio of 40 and dirty_background_ratio of 10 >> then that's good, but I'm sure if they knew you're moving dirty_ratio to 10 >> here, they'd want something like 2 for the dirty_background_ratio. >> >> I contend that the ratio between these two values is more important than >> their absolue values -- especially considering one gets twiddled here. > > > Maybe true, maybe false. These things are demonstrable via testing, no? > > Might be, I don't know how. Seemed straightforward (to me). -- 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-mm.org/ . Don't email: aart@kvack.org