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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6DEDAC433F5 for ; Wed, 2 Mar 2022 23:53:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229755AbiCBXxq (ORCPT ); Wed, 2 Mar 2022 18:53:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54488 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229735AbiCBXxo (ORCPT ); Wed, 2 Mar 2022 18:53:44 -0500 Received: from mailgw02.mediatek.com (unknown [210.61.82.184]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B63C3D1987; Wed, 2 Mar 2022 15:52:53 -0800 (PST) X-UUID: e55578293866465f8f422d077c288aa3-20220303 X-UUID: e55578293866465f8f422d077c288aa3-20220303 Received: from mtkcas11.mediatek.inc [(172.21.101.40)] by mailgw02.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-SHA384 256/256) with ESMTP id 342637879; Thu, 03 Mar 2022 07:52:45 +0800 Received: from mtkcas11.mediatek.inc (172.21.101.40) by mtkmbs10n2.mediatek.inc (172.21.101.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.792.3; Thu, 3 Mar 2022 07:52:43 +0800 Received: from mtksdccf07.mediatek.inc (172.21.84.99) by mtkcas11.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Thu, 3 Mar 2022 07:52:43 +0800 From: Miles Chen To: CC: , , , , , , , , , , , Subject: Re: [PATCH v2] iommu/iova: Reset max32_alloc_size after cleaning Date: Thu, 3 Mar 2022 07:52:38 +0800 Message-ID: <20220302235238.13099-1-miles.chen@mediatek.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain X-MTK: N Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >> If no cached iova is freed, resetting max32_alloc_size before >> the retry allocation only give us a retry. Is it possible that >> other users free their iovas during the additional retry? > > No, it's not possible, since everyone's serialised by iova_rbtree_lock. > If the caches were already empty and the retry gets the lock first, it > will still fail again - forcing a reset of max32_alloc_size only means > it has to take the slow path to that failure. If another caller *did* > manage to get in and free something between free_global_cached_iovas() > dropping the lock and alloc_iova() re-taking it, then that would have > legitimately reset max32_alloc_size anyway. Thanks for your explanation. YF showed me some numbers yesterday and maybe we can have a further discussion in that test case. (It looks like that some iovas are freed but their pfn_lo(s) are less than cached_iova->pfn_lo, so max32_alloc_size is not reset. So there are enought free iovas but the allocation still failed) __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free) { struct iova *cached_iova; cached_iova = to_iova(iovad->cached32_node); if (free == cached_iova || (free->pfn_hi < iovad->dma_32bit_pfn && free->pfn_lo >= cached_iova->pfn_lo)) { iovad->cached32_node = rb_next(&free->node); iovad->max32_alloc_size = iovad->dma_32bit_pfn; } ... } Hi YF, Could your share your observation of the iova allocation failure you hit? Thanks, Miles