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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6DBB2CD98F0 for ; Sun, 21 Jun 2026 20:49:41 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DD2966B0088; Sun, 21 Jun 2026 16:49:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D82BD6B008A; Sun, 21 Jun 2026 16:49:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BFFCD6B008C; Sun, 21 Jun 2026 16:49:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 877B56B0088 for ; Sun, 21 Jun 2026 16:49:39 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 0EADE1C546D for ; Sun, 21 Jun 2026 20:49:39 +0000 (UTC) X-FDA: 84905110878.12.2F29399 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf28.hostedemail.com (Postfix) with ESMTP id 4AA4CC0009 for ; Sun, 21 Jun 2026 20:49:36 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="g6iAM/3x"; spf=pass (imf28.hostedemail.com: domain of willy@infradead.org designates 90.155.50.34 as permitted sender) smtp.mailfrom=willy@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782074977; b=K6t5VTClf2Ahr2BikeptaCHMv3o8UFW1wmroFzHscOiSQ+G6ZcZhLH+wj1rBlfrHdafZDd aF/5+31gcMUV5tQ9Av83uwKcHs9HPr788djZ5OzUfdpq4Y0M4lO2wCgyxBKpTzwN8SGrfy TN//aQ+0ZTzVKHnRvocT5I3Kop3kS0Y= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="g6iAM/3x"; spf=pass (imf28.hostedemail.com: domain of willy@infradead.org designates 90.155.50.34 as permitted sender) smtp.mailfrom=willy@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782074977; 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:in-reply-to:references:references:dkim-signature; bh=M8eA5erpVUaElEed48rJS2wGTR5+Yv1nLd38ESSS2Rw=; b=mvWIjJwJAkye8tnyPZMH9m5IbOqKHe1WsnbfiV3vU5/Vdp2iZq69P9JfPH0im0l4pp9tXO RX1C8kjWpa6D0WbN73CWK3k2bJMYutDbG3uuR+EFi10cnY1afYCWIeFL8OnDIuDJ8HOqsT EPCGh7VFM3NS34JXoRYRwSUg2vVSb6w= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=M8eA5erpVUaElEed48rJS2wGTR5+Yv1nLd38ESSS2Rw=; b=g6iAM/3xDdWgV5X+yh4FkmLv62 OiHp0rJWKrS0azBEgV4lUi6tf73QIx3b1EfxkJWLE9+0vYHZwchHgBudDH0pHDxxXgTjwrWdu/mct Pv33b+2kvV7VjO9v7r9ZJhg42qZrzl0nH7+5lsv84CGZePPxYtNzgtc+jHFw/OqqVr5gfB6dJeyht Ta+Y3SqdvDLqXkzUCijftXQvtQR1xKMpDX3P8Pi4bp33DePJ+q2Ae6ol72ij7EXyHBJ2UsHVBJ0x9 +qUBkAxK1+zVPdKdmOAH0oG08P8SIzHjxBxu4r6NIyihQBFDoDV5qvDZCRzyYtm8IkqtseF10HUAj vqUbW0Ug==; Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wbP6X-00000002ysn-1JeK; Sun, 21 Jun 2026 20:49:21 +0000 Date: Sun, 21 Jun 2026 21:49:21 +0100 From: Matthew Wilcox To: Suren Baghdasaryan Cc: Barry Song , Lorenzo Stoakes , "David Hildenbrand (Arm)" , "Liam R. Howlett" , akpm@linux-foundation.org, linux-mm@kvack.org, vbabka@kernel.org, rppt@kernel.org, mhocko@suse.com, jack@suse.cz, pfalcato@suse.de, wanglian@kylinos.cn, chentao@kylinos.cn, lianux.mm@gmail.com, kunwu.chan@gmail.com, liyangouwen1@oppo.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, Nanzhe Zhao Subject: Re: [PATCH v2 0/5] mm: reduce mmap_lock contention and improve page fault performance Message-ID: References: <5zdaa5uv5oj27q3taopl3amops57ouxgyfsdveudz4ovmbdw7z@6lwrlyvmhcp2> <3be9475b-0e8a-4df8-a130-4262f993973d@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: fe9o8hptu4a537omic6qfwyo4z8mfxzo X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4AA4CC0009 X-HE-Tag: 1782074976-27785 X-HE-Meta: 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 X0KIKws6 vWcoWLXdbkoUXkXMWR7tj0djDAjTXl26u86HpJENG14iZK6nToT84GGVuWNcU0ZXEgKlbk9Solfe2/pJDrrDSQokeCc6Lbg7lzsUv94LgoDMduxGBBiUeZaKCe69RO6hqrtDGjovJOtKMN5crE86rLZA8n9ZjIt6byh+4Bpcanb0ooweX+XsbKWzPaQfVm46RoUwnnx1R4yp0a7taS1WGlPio2XG3zdIpG8tEO6IQKWvN/SicditOzJB8osvbWYWUaUTzDukILMWLkwyiJNJim6U+HTaiq/tUobtNManvjdqa2d8tsMDNcczhS7jvYo26qrksDp5egrjSsjSSjf2wpv+gVZBf04znxg8jUgZiO3CYwzDELbNLOVCh/g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jun 20, 2026 at 04:48:57PM -0700, Suren Baghdasaryan wrote: > Just checking in on the followup plans. IIUC the RFC mentioned will > try to implement the solution we discussed at LSFMM: splitting > VM_FAULT_RETRY into two flags - one for retrying under per-VMA locks > and another one to fallback to mmap_lock. I continue to hate this idea. I don't believe that those who were pushing for it have ever tried to understand the whole fault path. It's utterly byzantine. I defy anyone to make sense of this: /* * NOTE! This will make us return with VM_FAULT_RETRY, but with * the fault lock still held. That's how FAULT_FLAG_RETRY_NOWAIT * is supposed to work. We have way too many special cases.. */ if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) return 0; *fpin = maybe_unlock_mmap_for_io(vmf, *fpin); if (vmf->flags & FAULT_FLAG_KILLABLE) { if (__folio_lock_killable(folio)) { /* * We didn't have the right flags to drop the * fault lock, but all fault_handlers only check * for fatal signals if we return VM_FAULT_RETRY, * so we need to drop the fault lock here and * return 0 if we don't have a fpin. */ if (*fpin == NULL) release_fault_lock(vmf); return 0; } Wed need to simplify the fault path, not add additional complexity. Josef has said he wouldn't've done the lock dropping had we had per-VMA locks. We should rip it out.