From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail3-164.sinamail.sina.com.cn (mail3-164.sinamail.sina.com.cn [202.108.3.164]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5E9694A23 for ; Sun, 6 Sep 2026 03:50:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=202.108.3.164 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788666661; cv=none; b=YIOe7O+PJCWJGE2b/+xy2p/C93GsCuXi4byH2rP/zlfPPFNtOx3YI7OUGQ5IxtziaEpMpeL3pP9VeJHy/9beWcsRHMSVJ+9zRp+u7W1l7n8QSObVv7kBjRN3ZuFEqXY4RtzgqCWR0JinnGp3GlP7/7VU1OFHqwNIHB5AnB/NXek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788666661; c=relaxed/simple; bh=U8xHrBZ7Q3BQXgnr2L0uMBgk7gt6wGxE+ax6mXKRsWU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mphFIKt/Qe3EaixxyK/AGHfSf75YvqQW5WKddJ4JQ3OaHxlATdwJZQ4i0rvYqJOSyv7HTmoOjs6KGZvaNcNU85q3q1X9tM+9bpOi3mwUsCBX3H7oLcBVrtZfLKHaz6qB6LYMB4sa3A/phM9oZyzgwBzZUniWuGJxmZgsdRHb2P8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com; spf=pass smtp.mailfrom=sina.com; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b=JN/5gj5E; arc=none smtp.client-ip=202.108.3.164 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sina.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b="JN/5gj5E" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sina.com; s=201208; t=1788666651; bh=PQxvNMzas3x+IlCCh6neBcmKorR8pDTgu0p5/v3lP/I=; h=From:Subject:Date:Message-ID; b=JN/5gj5Eb/xmgetxCpF9/zxwdSUoRmba42u/q3L2Y/M4MgsRGtoKG7NkNPZeTaEkH N1iD3dk63nL/qyFj6IPbu5vJ6zHo2TAGGWjxhoNRq99sIySsfqEYEtvz8i9uhHjBra RR06aYgCYuUb9Xz6fTpbBDCFtfts0djB46Z9uStc= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([114.249.62.194]) by sina.com (10.54.253.32) with ESMTP id 6A9CE30D00007E2F; Sun, 6 Sep 2026 11:50:40 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 6954354456958 X-SMAIL-UIID: 553362F731704953BFFB61FDF2BADA41-20260906-115040-1 From: Hillf Danton To: "Uladzislau Rezki (Sony)" Cc: linux-mm@kvack.org, Baoquan He , LKML , stable@vger.kernel.org, Dev Jain , Ye Liu , lirongqing , Andrew Morton Subject: Re: [PATCH RESEND] mm/vmalloc: Use dedicated unbound workqueues for vmap drain Date: Sun, 6 Sep 2026 11:50:24 +0800 Message-ID: <20260906035027.2106-1-hdanton@sina.com> In-Reply-To: <20260905152717.11711-1-urezki@gmail.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Sat, 5 Sep 2026 17:27:17 +0200 "Uladzislau Rezki (Sony)" wrote: > drain_vmap_area_work() function can take >10ms to complete > when there are many accumulated vmap areas in a system with > high CPU count, causing workqueue watchdog warnings when run > via schedule_work(): > > workqueue: drain_vmap_area_work hogged CPU for >10000us > > Move the top-level drain work to a dedicated WQ_UNBOUND > workqueue so the scheduler can run this background work > on any available CPU, improving responsiveness. Use the > WQ_MEM_RECLAIM to ensure forward progress under memory > pressure. > If the dedicated worker will run for 4ms on CPU2 before the tick irq kicks it off cpu, the system event worker on CPU2 has to wait at least for 4ms to handle 200 events for example in 1ms, the net effect is the same as the current scenario where 200 events wait for the drain_vmap_area_work to complete on CPU1. Different workers does not help to dramatically decrement the micro seconds the drain_vmap_area_work takes.