From: Mel Gorman <mel@csn.ul.ie> To: Dave Hansen <dave@linux.vnet.ibm.com> Cc: Linux Memory Management List <linux-mm@kvack.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Nick Piggin <npiggin@suse.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Lin Ming <ming.m.lin@intel.com>, Zhang Yanmin <yanmin_zhang@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, Pekka Enberg <penberg@cs.helsinki.fi>, Andrew Morton <akpm@linux-foundation.org> Subject: Re: [PATCH 02/22] Do not sanity check order in the fast path Date: Wed, 22 Apr 2009 18:11:51 +0100 [thread overview] Message-ID: <20090422171151.GF15367@csn.ul.ie> (raw) In-Reply-To: <1240416791.10627.78.camel@nimitz> On Wed, Apr 22, 2009 at 09:13:11AM -0700, Dave Hansen wrote: > On Wed, 2009-04-22 at 14:53 +0100, Mel Gorman wrote: > > No user of the allocator API should be passing in an order >= MAX_ORDER > > but we check for it on each and every allocation. Delete this check and > > make it a VM_BUG_ON check further down the call path. > > Should we get the check re-added to some of the upper-level functions, > then? Perhaps __get_free_pages() or things like alloc_pages_exact()? > I don't think so, no. It just moves the source of the text bloat and for the few callers that are asking for something that will never succeed. > I'm selfishly thinking of what I did in profile_init(). Can I slab > alloc it? Nope. Page allocator? Nope. Oh, well, try vmalloc(): > > prof_buffer = kzalloc(buffer_bytes, GFP_KERNEL); > if (prof_buffer) > return 0; > > prof_buffer = alloc_pages_exact(buffer_bytes, GFP_KERNEL|__GFP_ZERO); > if (prof_buffer) > return 0; > > prof_buffer = vmalloc(buffer_bytes); > if (prof_buffer) > return 0; > > free_cpumask_var(prof_cpu_mask); > return -ENOMEM; > Can this ever actually be asking for an order larger than MAX_ORDER though? If so, you're condemning it to always behave poorly. > Same thing in __kmalloc_section_memmap(): > > page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size)); > if (page) > goto got_map_page; > > ret = vmalloc(memmap_size); > if (ret) > goto got_map_ptr; > If I'm reading that right, the order will never be a stupid order. It can fail for higher orders in which case it falls back to vmalloc() . For example, to hit that limit, the section size for a 4K kernel, maximum usable order of 10, the section size would need to be 256MB (assuming struct page size of 64 bytes). I don't think it's ever that size and if so, it'll always be sub-optimal which is a poor choice to make. > I depend on the allocator to tell me when I've fed it too high of an > order. If we really need this, perhaps we should do an audit and then > add a WARN_ON() for a few releases to catch the stragglers. > I consider it buggy to ask for something so large that you always end up with the worst option - vmalloc(). How about leaving it as a VM_BUG_ON to get as many reports as possible on who is depending on this odd behaviour? If there are users with good reasons, then we could convert this to WARN_ON to fix up the callers. I suspect that the allocator can already cope with recieving a stupid order silently but slowly. It should go all the way to the bottom and just never find anything useful and return NULL. zone_watermark_ok is the most dangerous looking part but even it should never get to MAX_ORDER because it should always find there are not enough free pages and return before it overruns. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mel@csn.ul.ie> To: Dave Hansen <dave@linux.vnet.ibm.com> Cc: Linux Memory Management List <linux-mm@kvack.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Nick Piggin <npiggin@suse.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Lin Ming <ming.m.lin@intel.com>, Zhang Yanmin <yanmin_zhang@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, Pekka Enberg <penberg@cs.helsinki.fi>, Andrew Morton <akpm@linux-foundation.org> Subject: Re: [PATCH 02/22] Do not sanity check order in the fast path Date: Wed, 22 Apr 2009 18:11:51 +0100 [thread overview] Message-ID: <20090422171151.GF15367@csn.ul.ie> (raw) In-Reply-To: <1240416791.10627.78.camel@nimitz> On Wed, Apr 22, 2009 at 09:13:11AM -0700, Dave Hansen wrote: > On Wed, 2009-04-22 at 14:53 +0100, Mel Gorman wrote: > > No user of the allocator API should be passing in an order >= MAX_ORDER > > but we check for it on each and every allocation. Delete this check and > > make it a VM_BUG_ON check further down the call path. > > Should we get the check re-added to some of the upper-level functions, > then? Perhaps __get_free_pages() or things like alloc_pages_exact()? > I don't think so, no. It just moves the source of the text bloat and for the few callers that are asking for something that will never succeed. > I'm selfishly thinking of what I did in profile_init(). Can I slab > alloc it? Nope. Page allocator? Nope. Oh, well, try vmalloc(): > > prof_buffer = kzalloc(buffer_bytes, GFP_KERNEL); > if (prof_buffer) > return 0; > > prof_buffer = alloc_pages_exact(buffer_bytes, GFP_KERNEL|__GFP_ZERO); > if (prof_buffer) > return 0; > > prof_buffer = vmalloc(buffer_bytes); > if (prof_buffer) > return 0; > > free_cpumask_var(prof_cpu_mask); > return -ENOMEM; > Can this ever actually be asking for an order larger than MAX_ORDER though? If so, you're condemning it to always behave poorly. > Same thing in __kmalloc_section_memmap(): > > page = alloc_pages(GFP_KERNEL|__GFP_NOWARN, get_order(memmap_size)); > if (page) > goto got_map_page; > > ret = vmalloc(memmap_size); > if (ret) > goto got_map_ptr; > If I'm reading that right, the order will never be a stupid order. It can fail for higher orders in which case it falls back to vmalloc() . For example, to hit that limit, the section size for a 4K kernel, maximum usable order of 10, the section size would need to be 256MB (assuming struct page size of 64 bytes). I don't think it's ever that size and if so, it'll always be sub-optimal which is a poor choice to make. > I depend on the allocator to tell me when I've fed it too high of an > order. If we really need this, perhaps we should do an audit and then > add a WARN_ON() for a few releases to catch the stragglers. > I consider it buggy to ask for something so large that you always end up with the worst option - vmalloc(). How about leaving it as a VM_BUG_ON to get as many reports as possible on who is depending on this odd behaviour? If there are users with good reasons, then we could convert this to WARN_ON to fix up the callers. I suspect that the allocator can already cope with recieving a stupid order silently but slowly. It should go all the way to the bottom and just never find anything useful and return NULL. zone_watermark_ok is the most dangerous looking part but even it should never get to MAX_ORDER because it should always find there are not enough free pages and return before it overruns. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2009-04-22 17:12 UTC|newest] Thread overview: 186+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-04-22 13:53 [PATCH 00/22] Cleanup and optimise the page allocator V7 Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 01/22] Replace __alloc_pages_internal() with __alloc_pages_nodemask() Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 02/22] Do not sanity check order in the fast path Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 16:13 ` Dave Hansen 2009-04-22 16:13 ` Dave Hansen 2009-04-22 17:11 ` Mel Gorman [this message] 2009-04-22 17:11 ` Mel Gorman 2009-04-22 17:30 ` Dave Hansen 2009-04-22 17:30 ` Dave Hansen 2009-04-23 0:13 ` Mel Gorman 2009-04-23 0:13 ` Mel Gorman 2009-04-23 1:34 ` Dave Hansen 2009-04-23 1:34 ` Dave Hansen 2009-04-23 9:58 ` Mel Gorman 2009-04-23 9:58 ` Mel Gorman 2009-04-23 17:36 ` Dave Hansen 2009-04-23 17:36 ` Dave Hansen 2009-04-24 2:57 ` KOSAKI Motohiro 2009-04-24 2:57 ` KOSAKI Motohiro 2009-04-24 10:34 ` Mel Gorman 2009-04-24 10:34 ` Mel Gorman 2009-04-24 14:16 ` Dave Hansen 2009-04-24 14:16 ` Dave Hansen 2009-04-23 19:26 ` Dave Hansen 2009-04-23 19:26 ` Dave Hansen 2009-04-23 19:45 ` Dave Hansen 2009-04-23 19:45 ` Dave Hansen 2009-04-24 9:21 ` Mel Gorman 2009-04-24 9:21 ` Mel Gorman 2009-04-24 14:25 ` Dave Hansen 2009-04-24 14:25 ` Dave Hansen 2009-04-22 20:11 ` David Rientjes 2009-04-22 20:11 ` David Rientjes 2009-04-22 20:20 ` Christoph Lameter 2009-04-22 20:20 ` Christoph Lameter 2009-04-23 7:44 ` Pekka Enberg 2009-04-23 7:44 ` Pekka Enberg 2009-04-23 22:44 ` Andrew Morton 2009-04-23 22:44 ` Andrew Morton 2009-04-22 13:53 ` [PATCH 03/22] Do not check NUMA node ID when the caller knows the node is valid Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 04/22] Check only once if the zonelist is suitable for the allocation Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 05/22] Break up the allocator entry point into fast and slow paths Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 06/22] Move check for disabled anti-fragmentation out of fastpath Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 07/22] Calculate the preferred zone for allocation only once Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-23 22:48 ` Andrew Morton 2009-04-23 22:48 ` Andrew Morton 2009-04-22 13:53 ` [PATCH 08/22] Calculate the migratetype " Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 09/22] Calculate the alloc_flags " Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-23 22:52 ` Andrew Morton 2009-04-23 22:52 ` Andrew Morton 2009-04-24 10:47 ` Mel Gorman 2009-04-24 10:47 ` Mel Gorman 2009-04-24 17:51 ` Andrew Morton 2009-04-24 17:51 ` Andrew Morton 2009-04-22 13:53 ` [PATCH 10/22] Remove a branch by assuming __GFP_HIGH == ALLOC_HIGH Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 11/22] Inline __rmqueue_smallest() Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 12/22] Inline buffered_rmqueue() Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 13/22] Inline __rmqueue_fallback() Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 14/22] Do not call get_pageblock_migratetype() more than necessary Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 15/22] Do not disable interrupts in free_page_mlock() Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-23 22:59 ` Andrew Morton 2009-04-23 22:59 ` Andrew Morton 2009-04-24 0:07 ` KOSAKI Motohiro 2009-04-24 0:07 ` KOSAKI Motohiro 2009-04-24 0:33 ` KOSAKI Motohiro 2009-04-24 0:33 ` KOSAKI Motohiro 2009-04-24 11:33 ` Mel Gorman 2009-04-24 11:33 ` Mel Gorman 2009-04-24 11:52 ` Lee Schermerhorn 2009-04-24 11:52 ` Lee Schermerhorn 2009-04-24 11:18 ` Mel Gorman 2009-04-24 11:18 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 16/22] Do not setup zonelist cache when there is only one node Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 20:24 ` David Rientjes 2009-04-22 20:24 ` David Rientjes 2009-04-22 20:32 ` Lee Schermerhorn 2009-04-22 20:32 ` Lee Schermerhorn 2009-04-22 20:34 ` David Rientjes 2009-04-22 20:34 ` David Rientjes 2009-04-23 0:11 ` KOSAKI Motohiro 2009-04-23 0:11 ` KOSAKI Motohiro 2009-04-23 0:19 ` Mel Gorman 2009-04-23 0:19 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 17/22] Do not check for compound pages during the page allocator sanity checks Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 18/22] Use allocation flags as an index to the zone watermark Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 17:11 ` Dave Hansen 2009-04-22 17:11 ` Dave Hansen 2009-04-22 17:14 ` Mel Gorman 2009-04-22 17:14 ` Mel Gorman 2009-04-22 17:47 ` Dave Hansen 2009-04-22 17:47 ` Dave Hansen 2009-04-23 0:27 ` KOSAKI Motohiro 2009-04-23 0:27 ` KOSAKI Motohiro 2009-04-23 10:03 ` Mel Gorman 2009-04-23 10:03 ` Mel Gorman 2009-04-24 6:41 ` KOSAKI Motohiro 2009-04-24 6:41 ` KOSAKI Motohiro 2009-04-22 20:06 ` David Rientjes 2009-04-22 20:06 ` David Rientjes 2009-04-23 0:29 ` Mel Gorman 2009-04-23 0:29 ` Mel Gorman 2009-04-27 17:00 ` [RFC] Replace the watermark-related union in struct zone with a watermark[] array Mel Gorman 2009-04-27 17:00 ` Mel Gorman 2009-04-27 20:48 ` David Rientjes 2009-04-27 20:48 ` David Rientjes 2009-04-27 20:54 ` Mel Gorman 2009-04-27 20:54 ` Mel Gorman 2009-04-27 20:51 ` Christoph Lameter 2009-04-27 20:51 ` Christoph Lameter 2009-04-27 21:04 ` David Rientjes 2009-04-27 21:04 ` David Rientjes 2009-04-30 13:35 ` Mel Gorman 2009-04-30 13:35 ` Mel Gorman 2009-04-30 13:48 ` Dave Hansen 2009-04-30 13:48 ` Dave Hansen 2009-05-12 14:13 ` [RFC] Replace the watermark-related union in struct zone with a watermark[] array V2 Mel Gorman 2009-05-12 14:13 ` Mel Gorman 2009-05-12 15:05 ` [RFC] Replace the watermark-related union in struct zone with awatermark[] " Dave Hansen 2009-05-12 15:05 ` Dave Hansen 2009-05-13 8:31 ` [RFC] Replace the watermark-related union in struct zone with a watermark[] " KOSAKI Motohiro 2009-05-13 8:31 ` KOSAKI Motohiro 2009-04-22 13:53 ` [PATCH 19/22] Update NR_FREE_PAGES only as necessary Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-23 23:06 ` Andrew Morton 2009-04-23 23:06 ` Andrew Morton 2009-04-23 23:04 ` Christoph Lameter 2009-04-23 23:04 ` Christoph Lameter 2009-04-24 13:06 ` Mel Gorman 2009-04-24 13:06 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 20/22] Get the pageblock migratetype without disabling interrupts Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 21/22] Use a pre-calculated value instead of num_online_nodes() in fast paths Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 23:04 ` David Rientjes 2009-04-22 23:04 ` David Rientjes 2009-04-23 0:44 ` Mel Gorman 2009-04-23 0:44 ` Mel Gorman 2009-04-23 19:29 ` David Rientjes 2009-04-23 19:29 ` David Rientjes 2009-04-24 13:31 ` [PATCH] Do not override definition of node_set_online() with macro Mel Gorman 2009-04-24 13:31 ` Mel Gorman 2009-04-22 13:53 ` [PATCH 22/22] slab: Use nr_online_nodes to check for a NUMA platform Mel Gorman 2009-04-22 13:53 ` Mel Gorman 2009-04-22 14:37 ` Pekka Enberg 2009-04-22 14:37 ` Pekka Enberg 2009-04-27 7:58 ` [PATCH 00/22] Cleanup and optimise the page allocator V7 Zhang, Yanmin 2009-04-27 7:58 ` Zhang, Yanmin 2009-04-27 14:38 ` Mel Gorman 2009-04-27 14:38 ` Mel Gorman 2009-04-28 1:59 ` Zhang, Yanmin 2009-04-28 1:59 ` Zhang, Yanmin 2009-04-28 10:27 ` Mel Gorman 2009-04-28 10:27 ` Mel Gorman 2009-04-28 10:31 ` [PATCH] Properly account for freed pages in free_pages_bulk() and when allocating high-order pages in buffered_rmqueue() Mel Gorman 2009-04-28 10:31 ` Mel Gorman 2009-04-28 16:37 ` Christoph Lameter 2009-04-28 16:37 ` Christoph Lameter 2009-04-28 16:51 ` Mel Gorman 2009-04-28 16:51 ` Mel Gorman 2009-04-28 17:15 ` Hugh Dickins 2009-04-28 17:15 ` Hugh Dickins 2009-04-28 18:07 ` [PATCH] Properly account for freed pages in free_pages_bulk() and when allocating high-order pages in buffered_rmqueue() V2 Mel Gorman 2009-04-28 18:07 ` Mel Gorman 2009-04-28 18:25 ` Hugh Dickins 2009-04-28 18:25 ` Hugh Dickins 2009-04-28 18:36 ` [PATCH] Properly account for freed pages in free_pages_bulk() and when allocating high-order pages in buffered_rmqueue() Mel Gorman 2009-04-28 18:36 ` Mel Gorman
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