From patchwork Thu Nov 7 23:56:10 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joanne Koong X-Patchwork-Id: 13867327 Received: from mail-yw1-f182.google.com (mail-yw1-f182.google.com [209.85.128.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F33511F4264 for ; Thu, 7 Nov 2024 23:56:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.182 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731023793; cv=none; b=bBg13uMnKLpKJs0junr4BfkZVqZ0xOSDPSMK76KC6TOXamPiHH+DXcHAYH4AyN3LZdNU+Geq1+EA5M9k8FYT39LDlCxo68nV3aCk+cQiAieTtR9Kdi2vtkTXtnfVk/jgp5VdlTWtih6B8VtqydsRxuB7HxcbQEp3vsX/9+pyyjk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731023793; c=relaxed/simple; bh=TNpy65gaPB+tGczJKWkCHgIevd+Hc74bVMSwhGgGHDk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BtL18w+Gxld4vx/BXPoCLq+I5XxRDm/Lfviy7QpHPYpfFzaanWA6oLtoMQQT8bI6NSa7B46XqvWFl/VCtIaw+sj/r1EMXq7UxbnnRIEa+OvR4uW5fSLS9pWOenKkfQEX6wfyion8IGrQwE1iexwjpfs01FmIp08w3F1QlebT7/8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=UTW21oxM; arc=none smtp.client-ip=209.85.128.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="UTW21oxM" Received: by mail-yw1-f182.google.com with SMTP id 00721157ae682-6e5e5c43497so12747017b3.3 for ; Thu, 07 Nov 2024 15:56:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1731023791; x=1731628591; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=kGp398/OGKFadKTdBHGJCLRTWw479TJgb4XjwbwuJpk=; b=UTW21oxMWvh6mUInUxCecvr6EaxB5uCiAX3fc68Csh20QmuIxZ/y8eAKzAxRk9zPIG SehQv5SgG82zUnbj5t3CZumgB7uxHXtHv6HwQUNTkWOiaAijwURFaiqBiKLT9lqWrdKE TekjBX/rf5yaUFcyBymgblSkk9XSz7e/65gz+sAinaO9VPUFL7Je9WEX69QLuY0UZxGD JrgO7fVCaX1grHTDNRYp7VGMdvXULLzYClqGfnIukOvlfXf+Cqh5dkViuctrNWfMp+hZ WcaFXxZ3Vg8gTHreoLOrYPvCEUyl3KOlh7eKn4Gq5ZUKUcIdIJTiGOj5TDFTesCQy8Mb BieQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1731023791; x=1731628591; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=kGp398/OGKFadKTdBHGJCLRTWw479TJgb4XjwbwuJpk=; b=ANJ/MFFeh2hBHQFDT0MO/GKsFD14GwK8c52MTXue/5gWAcey67G+dZQBO3XT2Cq603 LYFhenngUd1v90+5v6QxgvXnFCTB9b3s2h6vyvFtfaNGfrye7L3jkBobpB1IfoJ9S45i 85GWoVQCdQBZYVzSp0Lg6OAovBwnrMccWUQrIeGc7a4+BS1PKCfUFojHrYe4Hc966Jon GDZ7OnTZJ07ymj2YVJ2oCu0NkFx0Cd9H/+l69Iv4h9zjILetvnEpk+WRm9mVIqJnFEAl doYdIgu5h9FzghiRA568nYVvF0/f0TsQqhslbk2H8zvNYxdZpfD9tq/ziMPuC3r0BrwN LgxA== X-Forwarded-Encrypted: i=1; AJvYcCU8Rn3St4w0Uug8Jn1KQ2Kdu0nVrDgHQd67k/+cq+z1KpHL+qFeK8yxbeYxfTRhevynLF/ppuyvV0R+5EU0@vger.kernel.org X-Gm-Message-State: AOJu0Ywvhtc6CJmnD7pm894svHvZxxGs7Wr19GNOldRWPmG9+nwsV2lS RguTuVAL+zv+8t2N9ZeVq6e5eEs59DKiWIqq75HkUBIJp3amrs9r X-Google-Smtp-Source: AGHT+IGtwXdTUWVou6799sIkHT1OBBdHpywl7x1G3IHz/NTXy8iOQgd0OjfXXOssI2uPEUYjyoyP1g== X-Received: by 2002:a05:690c:4b8d:b0:6e3:8ecc:bb0e with SMTP id 00721157ae682-6eaddd94248mr12819677b3.11.1731023790878; Thu, 07 Nov 2024 15:56:30 -0800 (PST) Received: from localhost (fwdproxy-nha-012.fbsv.net. [2a03:2880:25ff:c::face:b00c]) by smtp.gmail.com with ESMTPSA id 00721157ae682-6eaceb6563bsm4999937b3.77.2024.11.07.15.56.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Nov 2024 15:56:30 -0800 (PST) From: Joanne Koong To: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org Cc: shakeel.butt@linux.dev, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, bernd.schubert@fastmail.fm, kernel-team@meta.com Subject: [PATCH v4 2/6] mm: skip reclaiming folios in legacy memcg writeback contexts that may block Date: Thu, 7 Nov 2024 15:56:10 -0800 Message-ID: <20241107235614.3637221-3-joannelkoong@gmail.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20241107235614.3637221-1-joannelkoong@gmail.com> References: <20241107235614.3637221-1-joannelkoong@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Currently in shrink_folio_list(), reclaim for folios under writeback falls into 3 different cases: 1) Reclaim is encountering an excessive number of folios under writeback and this folio has both the writeback and reclaim flags set 2) Dirty throttling is enabled (this happens if reclaim through cgroup is not enabled, if reclaim through cgroupv2 memcg is enabled, or if reclaim is on the root cgroup), or if the folio is not marked for immediate reclaim, or if the caller does not have __GFP_FS (or __GFP_IO if it's going to swap) set 3) Legacy cgroupv1 encounters a folio that already has the reclaim flag set and the caller did not have __GFP_FS (or __GFP_IO if swap) set In cases 1) and 2), we activate the folio and skip reclaiming it while in case 3), we wait for writeback to finish on the folio and then try to reclaim the folio again. In case 3, we wait on writeback because cgroupv1 does not have dirty folio throttling, as such this is a mitigation against the case where there are too many folios in writeback with nothing else to reclaim. The issue is that for filesystems where writeback may block, sub-optimal workarounds may need to be put in place to avoid a potential deadlock that may arise from reclaim waiting on writeback. (Even though case 3 above is rare given that legacy cgroupv1 is on its way to being deprecated, this case still needs to be accounted for). For example, for FUSE filesystems, a temp page gets allocated per dirty page and the contents of the dirty page are copied over to the temp page so that writeback can be immediately cleared on the dirty page in order to avoid the following deadlock: * single-threaded FUSE server is in the middle of handling a request that needs a memory allocation * memory allocation triggers direct reclaim * direct reclaim waits on a folio under writeback (eg falls into case 3 above) that needs to be written back to the FUSE server * the FUSE server can't write back the folio since it's stuck in direct reclaim In this commit, if legacy memcg encounters a folio with the reclaim flag set (eg case 3) and the folio belongs to a mapping that has the AS_WRITEBACK_MAY_BLOCK flag set, the folio will be activated and skip reclaim (eg default to behavior in case 2) instead. This allows for the suboptimal workarounds added to address the "reclaim wait on writeback" deadlock scenario to be removed. Signed-off-by: Joanne Koong Reviewed-by: Shakeel Butt --- mm/vmscan.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 749cdc110c74..e9755cb7211b 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1110,6 +1110,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, if (writeback && folio_test_reclaim(folio)) stat->nr_congested += nr_pages; + mapping = folio_mapping(folio); + /* * If a folio at the tail of the LRU is under writeback, there * are three cases to consider. @@ -1129,8 +1131,9 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, * 2) Global or new memcg reclaim encounters a folio that is * not marked for immediate reclaim, or the caller does not * have __GFP_FS (or __GFP_IO if it's simply going to swap, - * not to fs). In this case mark the folio for immediate - * reclaim and continue scanning. + * not to fs), or writebacks in the mapping may block. + * In this case mark the folio for immediate reclaim and + * continue scanning. * * Require may_enter_fs() because we would wait on fs, which * may not have submitted I/O yet. And the loop driver might @@ -1165,7 +1168,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, /* Case 2 above */ } else if (writeback_throttling_sane(sc) || !folio_test_reclaim(folio) || - !may_enter_fs(folio, sc->gfp_mask)) { + !may_enter_fs(folio, sc->gfp_mask) || + (mapping && mapping_writeback_may_block(mapping))) { /* * This is slightly racy - * folio_end_writeback() might have