From patchwork Thu Sep 8 12:50:37 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brian Geffon X-Patchwork-Id: 12970043 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D47F4C38145 for ; Thu, 8 Sep 2022 12:50:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0F3C08D0001; Thu, 8 Sep 2022 08:50:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0A37E6B0073; Thu, 8 Sep 2022 08:50:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EADBB8D0001; Thu, 8 Sep 2022 08:50:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id D7A196B0072 for ; Thu, 8 Sep 2022 08:50:47 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 9EA91121A37 for ; Thu, 8 Sep 2022 12:50:47 +0000 (UTC) X-FDA: 79888902534.19.79E6BB1 Received: from mail-il1-f202.google.com (mail-il1-f202.google.com [209.85.166.202]) by imf12.hostedemail.com (Postfix) with ESMTP id 3C6AA4008C for ; Thu, 8 Sep 2022 12:50:47 +0000 (UTC) Received: by mail-il1-f202.google.com with SMTP id k12-20020a92c24c000000b002f18edda397so8522869ilo.13 for ; Thu, 08 Sep 2022 05:50:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date; bh=OSiiUGLRIfq+vepm0vqg84Qq4WC9cX3015kZoVtJjwg=; b=gbJnz91nFa8X8hyQY9FW+AgwwvnIVWCUcxMkw17/xoagEJskEH7QQffjscIGLy7K+k xEM7BpHOCLQdCcTo9Lt3hrlqiLG1TyAl7fisd/7vteGn6Sg6TDRKpUSxCsU8rzqP19Jf HHAgNApy8T5P/9ZgFsKcaF4aLhFTFxYz7zQGPq5uzY4tWxyd8AFkXXiBn5uAp+11m9xY rMPZHwrO9gAfytoyxPxGMSlgzPDbfrCqoli8VThT6uehfaIH13zUJ5SjlUo2O5HMPBBn cazOxcKvQ76eZw0uC7F+/QzrETcozsBQ9e9FK0cXivP64hlMtoz+TUrA8iV5VfIv5hwa 05rQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date; bh=OSiiUGLRIfq+vepm0vqg84Qq4WC9cX3015kZoVtJjwg=; b=f0sCfsBNqwfUBWJr7r/mWo2ri6tjUyeIpPX0qSeC0/P3ZlV7I/OHQ5ABbesy25zjlQ Dnpl3yA5UqYmgdgfmdsbCzkhMsVWEIET9bhXVE5HMns3pTHjlmahuGtF/mKsDdu1VPzw kiGzR+g4lSIKmtS6IE6aLJ/Gzbl71leiMUUf1A4XD/j/VqosJ4TYKvvH5JBRbLws047C bgMGbMkEmSVsU2KxGinszaoFRFfOuW/9kmkC9shpWYyF9VnxtKHrWGQCeN86a6POR5DP KoD90/GHamfuqnO23ozw+zPyeHhPuoPA8jNGAa3exnF9zbAhXJd0TzvKqk9jVYYQ/7T/ oQsA== X-Gm-Message-State: ACgBeo0HpFS+AF3hBIEkxRujwOYzkKDAXRTfvs/+YIoWkI+ZvHKTad2w S22aM5cHE2ypLPE+CVH0mStDA1PHSybJ X-Google-Smtp-Source: AA6agR7X+KJs9M4HnSlcOLkLN+1xwYYWCrghj/R6JFYtigKnJK9HFvI4gt87055ZlwBSe3CD58pGJcSnnsoT X-Received: from bg.c.googlers.com ([fda3:e722:ac3:cc00:2b:ff92:c0a8:1b4]) (user=bgeffon job=sendgmr) by 2002:a05:6638:dc5:b0:350:b314:5ab1 with SMTP id m5-20020a0566380dc500b00350b3145ab1mr5020117jaj.256.1662641446435; Thu, 08 Sep 2022 05:50:46 -0700 (PDT) Date: Thu, 8 Sep 2022 08:50:37 -0400 Mime-Version: 1.0 X-Mailer: git-send-email 2.37.2.789.g6183377224-goog Message-ID: <20220908125037.1119114-1-bgeffon@google.com> Subject: [RESEND RFC] zram: Allow rw_page when page isn't written back. From: Brian Geffon To: Andrew Morton Cc: Minchan Kim , Nitin Gupta , Sergey Senozhatsky , linux-kernel@vger.kernel.org, Suleiman Souhlal , Rom Lemarchand , linux-mm@kvack.org, Brian Geffon ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=gbJnz91n; spf=pass (imf12.hostedemail.com: domain of 3JuUZYwcKCHcWbZaajibjjbgZ.Xjhgdips-hhfqVXf.jmb@flex--bgeffon.bounces.google.com designates 209.85.166.202 as permitted sender) smtp.mailfrom=3JuUZYwcKCHcWbZaajibjjbgZ.Xjhgdips-hhfqVXf.jmb@flex--bgeffon.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662641447; a=rsa-sha256; cv=none; b=Afa1hfsd1WrQ+FtHZIK6WJf+H6tcz8lsgaF+nqWwmAYSzf56riExpWTYpHAyuDnP6zrhv6 EJdnc/zKsDqCTEsY9qPyp0ipc4NQ2PrpmA6r9kVlLp321mooofaTIWfCJKeduVZVkOdssE fTZAITqdFo05I+eR9hYqfARXGNJliuU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662641447; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding:in-reply-to: references:dkim-signature; bh=OSiiUGLRIfq+vepm0vqg84Qq4WC9cX3015kZoVtJjwg=; b=7GTHM1TJwesjDqIgPcpJqocd/UaigaQc3ggK50ppQlF24NoH12/bJp802KHVMbtzzeeYgp ckwkqehyBm+TQ+6sZSKkPvSsmGze4l5zkHFYYqd/R0QMEmc2Y4kO/eLuZYkHJciqxqtH3i BFmjrr2nXt38iQmQfe6Clgl5uWk4Ph0= X-Rspamd-Queue-Id: 3C6AA4008C X-Rspam-User: Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=gbJnz91n; spf=pass (imf12.hostedemail.com: domain of 3JuUZYwcKCHcWbZaajibjjbgZ.Xjhgdips-hhfqVXf.jmb@flex--bgeffon.bounces.google.com designates 209.85.166.202 as permitted sender) smtp.mailfrom=3JuUZYwcKCHcWbZaajibjjbgZ.Xjhgdips-hhfqVXf.jmb@flex--bgeffon.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam01 X-Stat-Signature: 1saddnzejfj5hgi36bw418wuhy98det5 X-HE-Tag: 1662641447-841618 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Today when a zram device has a backing device we change the ops to a new set which does not expose a rw_page method. This prevents the upper layers from trying to issue a synchronous rw. This has the downside that we penalize every rw even when it could possibly still be performed as a synchronous rw. By the very nature of zram all writes are synchronous so it's unfortunate to have to accept this limitation. This change will always expose a rw_page function and if the page has been written back it will return -EOPNOTSUPP which will force the upper layers to try again with bio. To safely allow a synchronous read to proceed for pages which have not yet written back we introduce a new flag ZRAM_NO_WB. On the first synchronous read if the page is not written back we will set the ZRAM_NO_WB flag. This flag, which is never cleared, prevents writeback from ever happening to that page. This approach works because in the case of zram as a swap backing device the page is going to be removed from zram shortly thereafter so preventing writeback is fine. However, if zram is being used as a generic block device then this might prevent writeback of the page. This proposal is still very much RFC, feedback would be appreciated. Signed-off-by: Brian Geffon --- drivers/block/zram/zram_drv.c | 68 +++++++++++++++++++++-------------- drivers/block/zram/zram_drv.h | 1 + 2 files changed, 43 insertions(+), 26 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 92cb929a45b7..22b69e8b6042 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -52,9 +52,6 @@ static unsigned int num_devices = 1; static size_t huge_class_size; static const struct block_device_operations zram_devops; -#ifdef CONFIG_ZRAM_WRITEBACK -static const struct block_device_operations zram_wb_devops; -#endif static void zram_free_page(struct zram *zram, size_t index); static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec, @@ -309,7 +306,8 @@ static void mark_idle(struct zram *zram, ktime_t cutoff) */ zram_slot_lock(zram, index); if (zram_allocated(zram, index) && - !zram_test_flag(zram, index, ZRAM_UNDER_WB)) { + !zram_test_flag(zram, index, ZRAM_UNDER_WB) && + !zram_test_flag(zram, index, ZRAM_NO_WB)) { #ifdef CONFIG_ZRAM_MEMORY_TRACKING is_idle = !cutoff || ktime_after(cutoff, zram->table[index].ac_time); #endif @@ -439,7 +437,6 @@ static void reset_bdev(struct zram *zram) filp_close(zram->backing_dev, NULL); zram->backing_dev = NULL; zram->bdev = NULL; - zram->disk->fops = &zram_devops; kvfree(zram->bitmap); zram->bitmap = NULL; } @@ -543,17 +540,6 @@ static ssize_t backing_dev_store(struct device *dev, zram->backing_dev = backing_dev; zram->bitmap = bitmap; zram->nr_pages = nr_pages; - /* - * With writeback feature, zram does asynchronous IO so it's no longer - * synchronous device so let's remove synchronous io flag. Othewise, - * upper layer(e.g., swap) could wait IO completion rather than - * (submit and return), which will cause system sluggish. - * Furthermore, when the IO function returns(e.g., swap_readpage), - * upper layer expects IO was done so it could deallocate the page - * freely but in fact, IO is going on so finally could cause - * use-after-free when the IO is really done. - */ - zram->disk->fops = &zram_wb_devops; up_write(&zram->init_lock); pr_info("setup backing device %s\n", file_name); @@ -722,7 +708,8 @@ static ssize_t writeback_store(struct device *dev, if (zram_test_flag(zram, index, ZRAM_WB) || zram_test_flag(zram, index, ZRAM_SAME) || - zram_test_flag(zram, index, ZRAM_UNDER_WB)) + zram_test_flag(zram, index, ZRAM_UNDER_WB) || + zram_test_flag(zram, index, ZRAM_NO_WB)) goto next; if (mode & IDLE_WRITEBACK && @@ -1226,6 +1213,10 @@ static void zram_free_page(struct zram *zram, size_t index) goto out; } + if (zram_test_flag(zram, index, ZRAM_NO_WB)) { + zram_clear_flag(zram, index, ZRAM_NO_WB); + } + /* * No memory is allocated for same element filled pages. * Simply clear same page flag. @@ -1654,6 +1645,40 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector, index = sector >> SECTORS_PER_PAGE_SHIFT; offset = (sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT; +#ifdef CONFIG_ZRAM_WRITEBACK + /* + * With writeback feature, zram does asynchronous IO so it's no longer + * synchronous device so let's remove synchronous io flag. Othewise, + * upper layer(e.g., swap) could wait IO completion rather than + * (submit and return), which will cause system sluggish. + * Furthermore, when the IO function returns(e.g., swap_readpage), + * upper layer expects IO was done so it could deallocate the page + * freely but in fact, IO is going on so finally could cause + * use-after-free when the IO is really done. + * + * If the page is not currently written back then we may proceed to + * read the page synchronously, otherwise, we must fail with + * -EOPNOTSUPP to force the upper layers to use a normal bio. + */ + zram_slot_lock(zram, index); + if (zram_test_flag(zram, index, ZRAM_WB) || + zram_test_flag(zram, index, ZRAM_UNDER_WB)) { + zram_slot_unlock(zram, index); + /* We cannot proceed with synchronous read */ + return -EOPNOTSUPP; + } + + /* + * Don't allow the page to be written back while we read it, + * this flag is never cleared. It shouldn't be a problem that + * we don't clear this flag because in the case of swap this + * page will be removed shortly after this read anyway. + */ + if (op == REQ_OP_READ) + zram_set_flag(zram, index, ZRAM_NO_WB); + zram_slot_unlock(zram, index); +#endif + bv.bv_page = page; bv.bv_len = PAGE_SIZE; bv.bv_offset = 0; @@ -1827,15 +1852,6 @@ static const struct block_device_operations zram_devops = { .owner = THIS_MODULE }; -#ifdef CONFIG_ZRAM_WRITEBACK -static const struct block_device_operations zram_wb_devops = { - .open = zram_open, - .submit_bio = zram_submit_bio, - .swap_slot_free_notify = zram_slot_free_notify, - .owner = THIS_MODULE -}; -#endif - static DEVICE_ATTR_WO(compact); static DEVICE_ATTR_RW(disksize); static DEVICE_ATTR_RO(initstate); diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index 158c91e54850..20e4c6a579e0 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -50,6 +50,7 @@ enum zram_pageflags { ZRAM_UNDER_WB, /* page is under writeback */ ZRAM_HUGE, /* Incompressible page */ ZRAM_IDLE, /* not accessed page since last idle marking */ + ZRAM_NO_WB, /* Do not allow page to be written back */ __NR_ZRAM_PAGEFLAGS, };