From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 91EC6C433FE for ; Thu, 14 Oct 2021 11:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6E82E610E6 for ; Thu, 14 Oct 2021 11:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231225AbhJNL6n (ORCPT ); Thu, 14 Oct 2021 07:58:43 -0400 Received: from outbound-smtp10.blacknight.com ([46.22.139.15]:46459 "EHLO outbound-smtp10.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230337AbhJNL6k (ORCPT ); Thu, 14 Oct 2021 07:58:40 -0400 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp10.blacknight.com (Postfix) with ESMTPS id 292811C39DE for ; Thu, 14 Oct 2021 12:56:35 +0100 (IST) Received: (qmail 5409 invoked from network); 14 Oct 2021 11:56:34 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.17.29]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 14 Oct 2021 11:56:34 -0000 Date: Thu, 14 Oct 2021 12:56:32 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Linux-MM , NeilBrown , Theodore Ts'o , Andreas Dilger , "Darrick J . Wong" , Matthew Wilcox , Michal Hocko , Dave Chinner , Rik van Riel , Johannes Weiner , Jonathan Corbet , Linux-fsdevel , LKML Subject: Re: [PATCH 2/8] mm/vmscan: Throttle reclaim and compaction when too may pages are isolated Message-ID: <20211014115632.GZ3959@techsingularity.net> References: <20211008135332.19567-1-mgorman@techsingularity.net> <20211008135332.19567-3-mgorman@techsingularity.net> <5e2c8c39-29d9-61be-049f-a408f62f5acf@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <5e2c8c39-29d9-61be-049f-a408f62f5acf@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 14, 2021 at 10:06:25AM +0200, Vlastimil Babka wrote: > On 10/8/21 15:53, Mel Gorman wrote: > > Page reclaim throttles on congestion if too many parallel reclaim instances > > have isolated too many pages. This makes no sense, excessive parallelisation > > has nothing to do with writeback or congestion. > > > > This patch creates an additional workqueue to sleep on when too many > > pages are isolated. The throttled tasks are woken when the number > > of isolated pages is reduced or a timeout occurs. There may be > > some false positive wakeups for GFP_NOIO/GFP_NOFS callers but > > the tasks will throttle again if necessary. > > > > [shy828301@gmail.com: Wake up from compaction context] > > Signed-off-by: Mel Gorman > > ... > > > diff --git a/mm/internal.h b/mm/internal.h > > index 90764d646e02..06d0c376efcd 100644 > > --- a/mm/internal.h > > +++ b/mm/internal.h > > @@ -45,6 +45,15 @@ static inline void acct_reclaim_writeback(struct page *page) > > __acct_reclaim_writeback(pgdat, page, nr_throttled); > > } > > > > +static inline void wake_throttle_isolated(pg_data_t *pgdat) > > +{ > > + wait_queue_head_t *wqh; > > + > > + wqh = &pgdat->reclaim_wait[VMSCAN_THROTTLE_ISOLATED]; > > + if (waitqueue_active(wqh)) > > + wake_up_all(wqh); > > Again, would it be better to wake up just one task to prevent possible > thundering herd? We can assume that that task will call too_many_isolated() > eventually to wake up the next one? Same problem as the writeback throttling, there is no prioritsation of light vs heavy allocators. > Although it seems strange that > too_many_isolated() is the place where we detect the situation for wake up. > Simpler than to hook into NR_ISOLATED decrementing I guess. > Simplier but more costly. Every decrement would have to check too_many_isolated(). I think the cost of that is too high given that the VMSCAN_THROTTLE_ISOLATED is relatively hard to trigger and the minority of throttling events. > > +} > > + > > vm_fault_t do_swap_page(struct vm_fault *vmf); > > > > void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > ... > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1006,11 +1006,10 @@ static void handle_write_error(struct address_space *mapping, > > unlock_page(page); > > } > > > > -static void > > -reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason, > > +void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason, > > long timeout) > > { > > - wait_queue_head_t *wqh = &pgdat->reclaim_wait; > > + wait_queue_head_t *wqh = &pgdat->reclaim_wait[reason]; > > It seems weird that later in this function we increase nr_reclaim_throttled > without distinguishing the reason, so effectively throttling for isolated > pages will trigger acct_reclaim_writeback() doing the NR_THROTTLED_WRITTEN > counting, although it's not related at all? Maybe either have separate > nr_reclaim_throttled counters per vmscan_throttle_state (if counter of > isolated is useful, I haven't seen the rest of series yet), or count only > VMSCAN_THROTTLE_WRITEBACK tasks? > Very good point, it would be more appropriate to only count the writeback reason. Diff on top is below. It'll cause minor conflicts later in the series. diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index ca65d6a64bdd..58a25d42c31c 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -849,7 +849,7 @@ typedef struct pglist_data { wait_queue_head_t kswapd_wait; wait_queue_head_t pfmemalloc_wait; wait_queue_head_t reclaim_wait[NR_VMSCAN_THROTTLE]; - atomic_t nr_reclaim_throttled; /* nr of throtted tasks */ + atomic_t nr_writeback_throttled;/* nr of writeback-throttled tasks */ unsigned long nr_reclaim_start; /* nr pages written while throttled * when throttling started. */ struct task_struct *kswapd; /* Protected by diff --git a/mm/internal.h b/mm/internal.h index 06d0c376efcd..3461a1055975 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -39,7 +39,7 @@ void __acct_reclaim_writeback(pg_data_t *pgdat, struct page *page, static inline void acct_reclaim_writeback(struct page *page) { pg_data_t *pgdat = page_pgdat(page); - int nr_throttled = atomic_read(&pgdat->nr_reclaim_throttled); + int nr_throttled = atomic_read(&pgdat->nr_writeback_throttled); if (nr_throttled) __acct_reclaim_writeback(pgdat, page, nr_throttled); diff --git a/mm/vmscan.c b/mm/vmscan.c index 6e198bbbd86a..29434d4fc1c7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1011,6 +1011,7 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason, { wait_queue_head_t *wqh = &pgdat->reclaim_wait[reason]; long ret; + bool acct_writeback = (reason == VMSCAN_THROTTLE_WRITEBACK); DEFINE_WAIT(wait); /* @@ -1022,7 +1023,8 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason, current->flags & (PF_IO_WORKER|PF_KTHREAD)) return; - if (atomic_inc_return(&pgdat->nr_reclaim_throttled) == 1) { + if (acct_writeback && + atomic_inc_return(&pgdat->nr_writeback_throttled) == 1) { WRITE_ONCE(pgdat->nr_reclaim_start, node_page_state(pgdat, NR_THROTTLED_WRITTEN)); } @@ -1030,7 +1032,9 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason, prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE); ret = schedule_timeout(timeout); finish_wait(wqh, &wait); - atomic_dec(&pgdat->nr_reclaim_throttled); + + if (acct_writeback) + atomic_dec(&pgdat->nr_writeback_throttled); trace_mm_vmscan_throttled(pgdat->node_id, jiffies_to_usecs(timeout), jiffies_to_usecs(timeout - ret), @@ -4349,7 +4353,7 @@ static int kswapd(void *p) WRITE_ONCE(pgdat->kswapd_order, 0); WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES); - atomic_set(&pgdat->nr_reclaim_throttled, 0); + atomic_set(&pgdat->nr_writeback_throttled, 0); for ( ; ; ) { bool ret;