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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 64B4FC369C2 for ; Wed, 23 Apr 2025 01:47:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A39366B0005; Tue, 22 Apr 2025 21:47:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9E8286B0007; Tue, 22 Apr 2025 21:47:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8B0306B0008; Tue, 22 Apr 2025 21:47:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 6ACE96B0005 for ; Tue, 22 Apr 2025 21:47:51 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id D869B1605B5 for ; Wed, 23 Apr 2025 01:47:51 +0000 (UTC) X-FDA: 83363622342.26.E4CD1DC Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) by imf09.hostedemail.com (Postfix) with ESMTP id 105DA140006 for ; Wed, 23 Apr 2025 01:47:49 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=linux.org.uk header.s=zeniv-20220401 header.b=eNXJyIDN; dmarc=pass (policy=none) header.from=zeniv.linux.org.uk; spf=none (imf09.hostedemail.com: domain of viro@ftp.linux.org.uk has no SPF policy when checking 62.89.141.173) smtp.mailfrom=viro@ftp.linux.org.uk ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1745372870; a=rsa-sha256; cv=none; b=49Ez8D7atEhNXQr4XfwVa2ajtblNq+ojlw1sEdKjV/em0zqm61DuiF7e7XKUZIi/z9f/k7 CE5NDajmQRQZaeX0RYmJVARbqxS7CPReGo83snY/cFHmUbW9HssDoXbnP1WovQoWMRrPnN zaHtwp+56tUkUmo087GOW4RK4RUX+HQ= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=linux.org.uk header.s=zeniv-20220401 header.b=eNXJyIDN; dmarc=pass (policy=none) header.from=zeniv.linux.org.uk; spf=none (imf09.hostedemail.com: domain of viro@ftp.linux.org.uk has no SPF policy when checking 62.89.141.173) smtp.mailfrom=viro@ftp.linux.org.uk ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1745372870; h=from:from:sender: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:in-reply-to:references:references:dkim-signature; bh=ixXzq8+5TfvN7F+ux1yI6+sVOid8sZuHH4LjcLJXpD0=; b=jZF2NTX8rqY7QG5ImyrFWp6LN/zKFDcktVddYlUDTjIWYFHTSjrx4++JyO0fOiX/ehXNyV KOSPrI/HI3vSgsPXYRk/3rAcy4uJouOBLuYejGxlYkf5GTtR1ZgCmppFRVz5Eto1SvVrWM 3LfjWe90jk3iO2wbsrVng1eQk/BNxvI= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ixXzq8+5TfvN7F+ux1yI6+sVOid8sZuHH4LjcLJXpD0=; b=eNXJyIDNtOHOuDmyCJa/qxs1wL gCVEqZlmqoXjhi3VQqwK7MxqBFr3hvzkGmUgyOD8hMchViTXJUDe5nYxEVmaw1M7NS4zArjE7Wlys Rb8Nmr8FAAEm6Blxri6GaIBQ9cLj85vXn93b+5CLjAi3LBKQn4haVtRskyoDYwrUOK9yTTWK8s7EC 4dN9j+G6QKh/rNL469Utn3ermbfqtR/GwRKCmBrDqmMBkUrMXSRdvfz7PVGGzHrq8JMsytOKuRDWD K+gs6MeVrXoV7bN6xFRwv1Xis7+BiivWzyM9EZzgHrzThNLCFyVHiCiVx3YaAUaq39e/teudPXlS2 Vt7cHJGQ==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u7PD2-00000008Ezu-0KLX; Wed, 23 Apr 2025 01:47:32 +0000 Date: Wed, 23 Apr 2025 02:47:32 +0100 From: Al Viro To: Dave Chinner Cc: Harry Yoo , Christoph Lameter , David Rientjes , Andrew Morton , Roman Gushchin , "Tobin C. Harding" , Matthew Wilcox , Vlastimil Babka , Rik van Riel , Andrea Arcangeli , "Liam R. Howlett" , Lorenzo Stoakes , Jann Horn , Pedro Falcato , David Hildenbrand , Oscar Salvador , Michal Hocko , Byungchul Park , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [DISCUSSION] Revisiting Slab Movable Objects Message-ID: <20250423014732.GC2023217@ZenIV> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 105DA140006 X-Rspamd-Server: rspam04 X-Stat-Signature: ft9hk59huukcqft8hk1b6ykdyzhbbz6t X-HE-Tag: 1745372869-534090 X-HE-Meta: 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 FJFyEytP QiSMAJbb5ce2Tc12C/ktoZlkCx70547+HsIwgOxHf7LdZBpjAs08bB430sh/kc6z8kXDwQlJ8YTofg3ahyVOE2DtA3TLtY+JZtY2j0n3nZ+h8na4ko/N0apubW5wILr1ATI0gaEG/BiNt+B8= 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: List-Subscribe: List-Unsubscribe: On Tue, Apr 22, 2025 at 07:54:08AM +1000, Dave Chinner wrote: > I don't have a solution for the dentry cache reference issues - the > dentry cache maintains the working set of files, so anything that > randomly shoots down unused dentries for compaction is likely to > have negative performance implications for dentry cache intensive > workloads. Just to restate the obvious: _relocation_ of dentries is hopeless for many, many reasons - starting with "hash of dentry depends upon the address of its parent dentry". Freeing anything with zero refcount... sure, no problem - assuming that you are holding rcu_read_lock(), if (READ_ONCE(dentry->d_count) == 0) { spin_lock(&dentry->d_lock); if (dentry->d_count == 0) to_shrink_list(dentry, list); spin_unlock(&dentry->d_lock); } followed by rcu_read_unlock() and shrink_dentry_list(&list) once you are done collecting the candidates. If you want to wait for them to actually freed, synchronize_rcu() after rcu_read_unlock() (freeing is RCU-delayed). Performance implications are separate story - it really depends upon a lot of details. But simple "I want all unused dentries in this page kicked out" is doable. And in-use dentries are no-go, no matter what.