Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S272916AbTHEWOb (ORCPT ); Tue, 5 Aug 2003 18:14:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S272920AbTHEWOb (ORCPT ); Tue, 5 Aug 2003 18:14:31 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:43508 "EHLO hermes.mvista.com") by vger.kernel.org with ESMTP id S272916AbTHEWOI (ORCPT ); Tue, 5 Aug 2003 18:14:08 -0400 Subject: [patch] real-time enhanced page allocator and throttling From: Robert Love To: akpm@osdl.org, linux-kernel@vger.kernel.org Cc: Valdis.Kletnieks@vt.edu, piggin@cyberone.com.au, kernel@kolivas.org, linux-mm@kvack.org Content-Type: text/plain Message-Id: <1060121638.4494.111.camel@localhost> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.3 (1.4.3-5) Date: 05 Aug 2003 15:13:59 -0700 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5979 Lines: 176 On Mon, 2003-08-04 at 22:55, Andrew Morton wrote: > There is a very good argument for giving !SCHED_OTHER tasks > "special treatment" in the VM. Yes, there is. Attached patch is against 2.6.0-test2-mm4. It does two main things: - Let real-time tasks dip further into the reserves than usual in __alloc_pages(). There are a lot of ways to special case this. This patch just cuts z->pages_low in half, before doing the incremental min thing, for real-time tasks. I do not do anything in the low memory slow path. We can be a _lot_ more aggressive if we want. Right now, we just give real-time tasks a little help. - Never ever call balance_dirty_pages() on a real-time task. Where and how exactly we handle this is up for debate. We could, for example, special case real-time tasks inside balance_dirty_pages(). This would allow us to perform some of the work (say, waking up pdflush) but not other work (say, the active throttling). As it stands now, we do the per-processor accounting in balance_dirty_pages_ratelimited() but we never call balance_dirty_pages(). Lots of approaches work. What we want to do is never engage the real-time task in forced writeback. It compiles, it boots, and it does not crash. I have not tested whether it prevents any starvation in real-time applications that are being observed -- mostly because I am not sure if my approach is what you want. There are multiple ways to handle the real-time task path. I picked one. I do not know. Robert Love include/linux/sched.h | 4 +++- kernel/sched.c | 1 - mm/page-writeback.c | 6 +++++- mm/page_alloc.c | 29 ++++++++++++++++++++--------- 4 files changed, 28 insertions(+), 12 deletions(-) diff -urN linux-2.6.0-test2-mm4/include/linux/sched.h linux/include/linux/sched.h --- linux-2.6.0-test2-mm4/include/linux/sched.h 2003-08-05 14:53:47.000000000 -0700 +++ linux/include/linux/sched.h 2003-08-05 12:38:41.000000000 -0700 @@ -282,7 +282,9 @@ #define MAX_RT_PRIO MAX_USER_RT_PRIO #define MAX_PRIO (MAX_RT_PRIO + 40) - + +#define rt_task(p) ((p)->prio < MAX_RT_PRIO) + /* * Some day this will be a full-fledged user tracking system.. */ diff -urN linux-2.6.0-test2-mm4/kernel/sched.c linux/kernel/sched.c --- linux-2.6.0-test2-mm4/kernel/sched.c 2003-08-05 14:53:47.000000000 -0700 +++ linux/kernel/sched.c 2003-08-05 12:38:29.000000000 -0700 @@ -199,7 +199,6 @@ #define this_rq() (cpu_rq(smp_processor_id())) /* not __get_cpu_var(runqueues)! */ #define task_rq(p) cpu_rq(task_cpu(p)) #define cpu_curr(cpu) (cpu_rq(cpu)->curr) -#define rt_task(p) ((p)->prio < MAX_RT_PRIO) /* * Default context-switch locking: diff -urN linux-2.6.0-test2-mm4/mm/page_alloc.c linux/mm/page_alloc.c --- linux-2.6.0-test2-mm4/mm/page_alloc.c 2003-08-05 14:48:38.000000000 -0700 +++ linux/mm/page_alloc.c 2003-08-05 14:40:56.000000000 -0700 @@ -518,7 +518,8 @@ * * Herein lies the mysterious "incremental min". That's the * - * min += z->pages_low; + * local_low = z->pages_low; + * min += local_low; * * thing. The intent here is to provide additional protection to low zones for * allocation requests which _could_ use higher zones. So a GFP_HIGHMEM @@ -536,10 +537,11 @@ unsigned long min; struct zone **zones, *classzone; struct page *page; + struct reclaim_state reclaim_state; + struct task_struct *p = current; int i; int cold; int do_retry; - struct reclaim_state reclaim_state; if (wait) might_sleep(); @@ -557,8 +559,17 @@ min = 1UL << order; for (i = 0; zones[i] != NULL; i++) { struct zone *z = zones[i]; + unsigned long local_low; + + /* + * This is the fabled 'incremental min'. We let real-time tasks + * dip their real-time paws a little deeper into reserves. + */ + local_low = z->pages_low; + if (rt_task(p)) + local_low >>= 1; + min += local_low; - min += z->pages_low; if (z->free_pages >= min || (!wait && z->free_pages >= z->pages_high)) { page = buffered_rmqueue(z, order, cold); @@ -594,7 +605,7 @@ /* here we're in the low on memory slow path */ rebalance: - if ((current->flags & (PF_MEMALLOC | PF_MEMDIE)) && !in_interrupt()) { + if ((p->flags & (PF_MEMALLOC | PF_MEMDIE)) && !in_interrupt()) { /* go through the zonelist yet again, ignoring mins */ for (i = 0; zones[i] != NULL; i++) { struct zone *z = zones[i]; @@ -610,14 +621,14 @@ if (!wait) goto nopage; - current->flags |= PF_MEMALLOC; + p->flags |= PF_MEMALLOC; reclaim_state.reclaimed_slab = 0; - current->reclaim_state = &reclaim_state; + p->reclaim_state = &reclaim_state; try_to_free_pages(classzone, gfp_mask, order); - current->reclaim_state = NULL; - current->flags &= ~PF_MEMALLOC; + p->reclaim_state = NULL; + p->flags &= ~PF_MEMALLOC; /* go through the zonelist yet one more time */ min = 1UL << order; @@ -657,7 +668,7 @@ if (!(gfp_mask & __GFP_NOWARN)) { printk("%s: page allocation failure." " order:%d, mode:0x%x\n", - current->comm, order, gfp_mask); + p->comm, order, gfp_mask); } return NULL; got_pg: diff -urN linux-2.6.0-test2-mm4/mm/page-writeback.c linux/mm/page-writeback.c --- linux-2.6.0-test2-mm4/mm/page-writeback.c 2003-08-05 14:53:47.000000000 -0700 +++ linux/mm/page-writeback.c 2003-08-05 13:48:43.000000000 -0700 @@ -227,7 +227,11 @@ if (dirty_exceeded) ratelimit = 8; - if (get_cpu_var(ratelimits)++ >= ratelimit) { + /* + * Check the rate limiting. Also, we do not want to throttle real-time + * tasks in balance_dirty_pages(). Period. + */ + if (get_cpu_var(ratelimits)++ >= ratelimit && !rt_task(current)) { __get_cpu_var(ratelimits) = 0; put_cpu_var(ratelimits); return balance_dirty_pages(mapping); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/