From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-202.mailbox.org (mout-p-202.mailbox.org [80.241.56.172]) (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 112FA233159; Fri, 16 May 2025 10:11:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747390284; cv=none; b=ip7F9i0heTFwra0JzzbbkpXEHupPid/4CRJPIjdQMaqtjJokn/BxjWwOgbtWPZv0DdqADt2kDk6Jo+45R4xkGJ/GhZkhIhhyExHkp5XcC5NE0wK91bBMapSB3AbcbFinET2TTLpRsm+svi5stsGNyNXYunm+HI7Hw8UJF2sjILs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747390284; c=relaxed/simple; bh=aaTOj7kfhFSOVIoJP8tXQ3B2wT5QtcvJnD+E2EI11lw=; h=From:To:Cc:Subject:Date:Message-ID:Content-Type:MIME-Version; b=JAlY2PYXcKMEuTGJibYlbyCZVDmUVMO5oy8/kuv+TcmI8aF1xlXuPXsA3tvSTE3And4i9rz/I+812AUA1birqwO8b9r+lLkqnnDP62m6H9e5OVt83Vp9TaaJJ4ITHRUfaQMr9RXro758U8b761wXU8b6Zzpm7zw7Zus6xOiCaeg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=samsung.com; spf=pass smtp.mailfrom=pankajraghav.com; arc=none smtp.client-ip=80.241.56.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=samsung.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pankajraghav.com Received: from smtp202.mailbox.org (smtp202.mailbox.org [IPv6:2001:67c:2050:b231:465::202]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-202.mailbox.org (Postfix) with ESMTPS id 4ZzNC35VRsz9stK; Fri, 16 May 2025 12:11:11 +0200 (CEST) From: Pankaj Raghav To: "Darrick J . Wong" , hch@lst.de, willy@infradead.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, David Hildenbrand , linux-fsdevel@vger.kernel.org, mcgrof@kernel.org, gost.dev@samsung.com, Andrew Morton , kernel@pankajraghav.com, Pankaj Raghav Subject: [RFC 0/3] add large zero page for zeroing out larger segments Date: Fri, 16 May 2025 12:10:51 +0200 Message-ID: <20250516101054.676046-1-p.raghav@samsung.com> Content-Type: text/plain; charset="utf-8" Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 4ZzNC35VRsz9stK Introduce LARGE_ZERO_PAGE of size 2M as an alternative to ZERO_PAGE. Similar to ZERO_PAGE, LARGE_ZERO_PAGE is also a global shared page. 2M seems to be a decent compromise between memory usage and performance. This idea (but not the implementation) was suggested during the review of adding LBS support to XFS[1][2]. NOTE: === This implementation probably has a lot of holes, and it is not complete. For example, this implementation only works on x86. The intent of the RFC is: - To understand if this is something we still need in the kernel. - If this is the approach we want to take to implement a feature like this or should we explore other alternatives. I have excluded a lot of Maintainers/mailing list and only included relevant folks in this RFC to understand the direction we want to take if this feature is needed. === There are many places in the kernel where we need to zeroout larger chunks but the maximum segment we can zeroout at a time is limited by PAGE_SIZE. This is especially annoying in block devices and filesystems where we attach multiple ZERO_PAGEs to the bio in different bvecs. With multipage bvec support in block layer, it is much more efficient to send out larger zero pages as a part of a single bvec. Some examples of places in the kernel where this could be useful: - blkdev_issue_zero_pages() - iomap_dio_zero() - vmalloc.c:zero_iter() - rxperf_process_call() - fscrypt_zeroout_range_inline_crypt() - bch2_checksum_update() ... I have converted blkdev_issue_zero_pages() and iomap_dio_zero() as an example as a part of this series. While there are other options such as huge_zero_page, they can fail based on the system conditions requiring a fallback to ZERO_PAGE[3]. LARGE_ZERO_PAGE is added behind a config option so that systems that are constrained by memory are not forced to use it. Looking forward to some feedback. [1] https://lore.kernel.org/linux-xfs/20231027051847.GA7885@lst.de/ [2] https://lore.kernel.org/linux-xfs/ZitIK5OnR7ZNY0IG@infradead.org/ Pankaj Raghav (3): mm: add large zero page for efficient zeroing of larger segments block: use LARGE_ZERO_PAGE in __blkdev_issue_zero_pages() iomap: use LARGE_ZERO_PAGE in iomap_dio_zero() arch/Kconfig | 8 ++++++++ arch/x86/include/asm/pgtable.h | 20 +++++++++++++++++++- arch/x86/kernel/head_64.S | 9 ++++++++- block/blk-lib.c | 4 ++-- fs/iomap/direct-io.c | 31 +++++++++---------------------- 5 files changed, 46 insertions(+), 26 deletions(-) base-commit: 9e619cd4fefd19cdce16e169d5827bc64ae01aa1 -- 2.47.2