From patchwork Fri Dec 18 17:01:48 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Robin Murphy X-Patchwork-Id: 7887161 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 231309F1AF for ; Fri, 18 Dec 2015 17:04:25 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 49A1E204D3 for ; Fri, 18 Dec 2015 17:04:24 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5D7E8200E0 for ; Fri, 18 Dec 2015 17:04:23 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1a9yQp-00038e-G4; Fri, 18 Dec 2015 17:03:03 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1a9yQ8-0002YG-7n for linux-arm-kernel@lists.infradead.org; Fri, 18 Dec 2015 17:02:23 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9B03F545; Fri, 18 Dec 2015 09:01:33 -0800 (PST) Received: from e104324-lin.cambridge.arm.com (e104324-lin.cambridge.arm.com [10.1.205.141]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 14E923F459; Fri, 18 Dec 2015 09:01:57 -0800 (PST) From: Robin Murphy To: joro@8bytes.org Subject: [PATCH 3/3] iommu/dma: Avoid unlikely high-order allocations Date: Fri, 18 Dec 2015 17:01:48 +0000 Message-Id: <8014a146e90282b8cbc5868cee0d01776670d9a6.1450457730.git.robin.murphy@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <9a84191ed813c23db7901f8c73f514d081495bdf.1450457730.git.robin.murphy@arm.com> References: <9a84191ed813c23db7901f8c73f514d081495bdf.1450457730.git.robin.murphy@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20151218_090220_601373_883F9152 X-CRM114-Status: GOOD ( 11.14 ) X-Spam-Score: -6.9 (------) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: iommu@lists.linux-foundation.org, dianders@chromium.org, linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Doug reports that the equivalent page allocator on 32-bit ARM exhibits particularly pathalogical behaviour under memory pressure when fragmentation is high, where allocating a 4MB buffer takes tens of seconds and the number of calls to alloc_pages() is over 9000![1] We can drastically improve that situation without losing the other benefits of high-order allocations when they would succeed, by assuming memory pressure is relatively constant over the course of an allocation, and not retrying allocations at orders we know to have failed before. This way, the best-case behaviour remains unchanged, and in the worst case we should see at most a dozen or so (MAX_ORDER - 1) failed attempts before falling back to single pages for the remainder of the buffer. [1]:http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/394660.html Reported-by: Douglas Anderson Signed-off-by: Robin Murphy --- drivers/iommu/dma-iommu.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c index 03811e3..e37516a 100644 --- a/drivers/iommu/dma-iommu.c +++ b/drivers/iommu/dma-iommu.c @@ -194,6 +194,7 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count, gfp_t gfp) { struct page **pages; unsigned int i = 0, array_size = count * sizeof(*pages); + unsigned int order = MAX_ORDER; if (array_size <= PAGE_SIZE) pages = kzalloc(array_size, GFP_KERNEL); @@ -207,14 +208,15 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count, gfp_t gfp) while (count) { struct page *page = NULL; - int j, order = __fls(count); + int j; /* * Higher-order allocations are a convenience rather * than a necessity, hence using __GFP_NORETRY until * falling back to single-page allocations. */ - for (order = min(order, MAX_ORDER); order > 0; order--) { + for (order = min_t(unsigned int, order, __fls(count)); + order > 0; order--) { page = alloc_pages(gfp | __GFP_NORETRY, order); if (!page) continue;