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Date: Thu, 16 Feb 2017 16:21:04 +0800 From: "Hillf Danton" <hillf.zj@...baba-inc.com> To: "'Mel Gorman'" <mgorman@...hsingularity.net> Cc: "'Andrew Morton'" <akpm@...ux-foundation.org>, "'Shantanu Goel'" <sgoel01@...oo.com>, "'Chris Mason'" <clm@...com>, "'Johannes Weiner'" <hannes@...xchg.org>, "'Vlastimil Babka'" <vbabka@...e.cz>, "'LKML'" <linux-kernel@...r.kernel.org>, "'Linux-MM'" <linux-mm@...ck.org> Subject: Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx On February 16, 2017 4:11 PM Mel Gorman wrote: > On Thu, Feb 16, 2017 at 02:23:08PM +0800, Hillf Danton wrote: > > On February 15, 2017 5:23 PM Mel Gorman wrote: > > > */ > > > static int kswapd(void *p) > > > { > > > - unsigned int alloc_order, reclaim_order, classzone_idx; > > > + unsigned int alloc_order, reclaim_order; > > > + unsigned int classzone_idx = MAX_NR_ZONES - 1; > > > pg_data_t *pgdat = (pg_data_t*)p; > > > struct task_struct *tsk = current; > > > > > > @@ -3447,20 +3466,23 @@ static int kswapd(void *p) > > > tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > > > set_freezable(); > > > > > > - pgdat->kswapd_order = alloc_order = reclaim_order = 0; > > > - pgdat->kswapd_classzone_idx = classzone_idx = 0; > > > + pgdat->kswapd_order = 0; > > > + pgdat->kswapd_classzone_idx = MAX_NR_ZONES; > > > for ( ; ; ) { > > > bool ret; > > > > > > + alloc_order = reclaim_order = pgdat->kswapd_order; > > > + classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx); > > > + > > > kswapd_try_sleep: > > > kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order, > > > classzone_idx); > > > > > > /* Read the new order and classzone_idx */ > > > alloc_order = reclaim_order = pgdat->kswapd_order; > > > - classzone_idx = pgdat->kswapd_classzone_idx; > > > + classzone_idx = kswapd_classzone_idx(pgdat, 0); > > > pgdat->kswapd_order = 0; > > > - pgdat->kswapd_classzone_idx = 0; > > > + pgdat->kswapd_classzone_idx = MAX_NR_ZONES; > > > > > > ret = try_to_freeze(); > > > if (kthread_should_stop()) > > > @@ -3486,9 +3508,6 @@ static int kswapd(void *p) > > > reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx); > > > if (reclaim_order < alloc_order) > > > goto kswapd_try_sleep; > > > > If we fail order-5 request, can we then give up order-5, and > > try order-3 if requested, after napping? > > > > That has no bearing upon this patch. At this point, kswapd has stopped > reclaiming at the requested order and is preparing to sleep. If there is > a parallel request for order-3 while it's sleeping, it'll wake and start > reclaiming at order-3 as requested. > Right, but the order-3 request can also come up while kswapd is active and gives up order-5. thanks Hillf
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