From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 8 May 2001 14:23:56 -0300 (BRT) From: Marcelo Tosatti Subject: Re: [PATCH] allocation looping + kswapd CPU cycles 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: Mark Hemment Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Tue, 8 May 2001, Mark Hemment wrote: > > In 2.4.3pre6, code in page_alloc.c:__alloc_pages(), changed from; > > try_to_free_pages(gfp_mask); > wakeup_bdflush(); > if (!order) > goto try_again; > to > try_to_free_pages(gfp_mask); > wakeup_bdflush(); > goto try_again; > > > This introduced the effect of a non-zero order, __GFP_WAIT allocation > (without PF_MEMALLOC set), never returning failure. The allocation keeps > looping in __alloc_pages(), kicking kswapd, until the allocation succeeds. > > If there is plenty of memory in the free-pools and inactive-lists > free_shortage() will return false, causing the state of these > free-pools/inactive-lists not to be 'improved' by kswapd. > > If there is nothing else changing/improving the free-pools or > inactive-lists, the allocation loops forever (kicking kswapd). > > Does anyone know why the 2.4.3pre6 change was made? Because wakeup_bdflush(0) can wakeup bdflush _even_ if it does not have any job to do (ie less than 30% dirty buffers in the default config). > > The attached patch (against 2.4.5-pre1) fixes the looping symptom, by > adding a counter and looping only twice for non-zero order allocations. Looks good. (actually Rik had a patch similar to this which fixed a real case with cdda2wav just like you described) -- 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/