From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D6C953EDAB8 for ; Tue, 31 Mar 2026 14:16:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774966567; cv=none; b=qlo8QQ8wvHtUReTEFMh7YFZbJCbqRiUYickZIVXEhcAgWseu5TusKRoPXJTG0vZq2MgH/6/FoSZu+QQe8mNoN0S42evwyJ91Jrda6TUZOPcs2XlnbSQ0wyofd//nZhdfmwWZ/oJCKwnbKUZPCqfxDhTa84SxM/deiM21E1s1ozY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774966567; c=relaxed/simple; bh=P+JOMuhq4U1b2iThGkPhI7G7/g5oR6RU6sBz2YvQW1I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DaTFtrWACGTnmkxohgi18/rupuzfPjpA3FRL8FWl7/jV292XHuYmoNpSxGqYEGL2xMPv6QmzrFIz2BiSjLP2gRr15s7wEf574PmqUykNJ79dgmn7ZzFl/kCOjowJn643eGqT2g24s6VPAua0zv3wkRuuSdY4hDptaMnQk3yEfsQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SNboa4Y6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SNboa4Y6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54175C19423; Tue, 31 Mar 2026 14:15:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774966567; bh=P+JOMuhq4U1b2iThGkPhI7G7/g5oR6RU6sBz2YvQW1I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SNboa4Y6IqQh1zqNeRcApl01cTc/UNKo3mGYLne8KJIgI4EckiJMCfe/Igf7lVlmF 01/yN8Vd/oc7QZ4dTEEuR1WlMwmkcqxhJc30YrV79BR6hPZYJCcYf42xHLoYcrhAxk QUetGq35k6EnEZVu0VwdC6JAiExy7n4q5zf17laIIToknXPDOnyDFLchaVRsQPaVjD lC9pkeEMIid+OmmRRBBksTmG8pwNgBqE0qg0ToVcdR3hSKbeIw2jM/ZCQ3588Uw4+5 vDLoXtcpwJcsI+9cFgnigzUN0ueIgApPvzjXCIRuRLS7ROcpSeBs3ztHwVWnAcMpnO 3riO/udH1Ra3g== Date: Tue, 31 Mar 2026 15:15:56 +0100 From: "Lorenzo Stoakes (Oracle)" To: "David Hildenbrand (Arm)" Cc: Nico Pache , linux-kernel@vger.kernel.org, linux-mm@kvack.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jackmanb@google.com, jack@suse.cz, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v4 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() Message-ID: References: <20260325114022.444081-1-npache@redhat.com> <20260325114022.444081-6-npache@redhat.com> <7760c811-e100-4d40-9217-0813c28314be@lucifer.local> <0223d45b-e8b4-49a7-882b-477250d0c14d@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0223d45b-e8b4-49a7-882b-477250d0c14d@kernel.org> On Tue, Mar 31, 2026 at 04:13:29PM +0200, David Hildenbrand (Arm) wrote: > >> + if (*lock_dropped) { > >> cond_resched(); > >> mmap_read_lock(mm); > >> - mmap_locked = true; > >> + *lock_dropped = false; > > > > So this is the bug. 'lock_dropped' needs to record if the lock was _ever_ > > dropped, not if it is _currently_ dropped. > > Ah, well spotted. I thought we discussed that at some point during > review ... > > Thanks for tackling this! > > [...] > > > > > ----8<---- > > From a4dfc7718a15035449f344a0bc7f58e449366405 Mon Sep 17 00:00:00 2001 > > From: "Lorenzo Stoakes (Oracle)" > > Date: Tue, 31 Mar 2026 13:11:18 +0100 > > Subject: [PATCH] mm/khugepaged: fix issue with tracking lock > > > > We are incorrectly treating lock_dropped to track both whether the lock is > > currently held and whether or not the lock was ever dropped. > > > > Update this change to account for this. > > > > Signed-off-by: Lorenzo Stoakes (Oracle) > > --- > > mm/khugepaged.c | 12 ++++++++---- > > 1 file changed, 8 insertions(+), 4 deletions(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index d21348b85a59..b8452dbdb043 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -2828,6 +2828,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > > unsigned long hstart, hend, addr; > > enum scan_result last_fail = SCAN_FAIL; > > int thps = 0; > > + bool mmap_unlocked = false; > > > > BUG_ON(vma->vm_start > start); > > BUG_ON(vma->vm_end < end); > > @@ -2850,10 +2851,11 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > > for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { > > enum scan_result result = SCAN_FAIL; > > > > - if (*lock_dropped) { > > + if (mmap_unlocked) { > > cond_resched(); > > mmap_read_lock(mm); > > - *lock_dropped = false; > > + mmap_unlocked = false; > > + *lock_dropped = true; > > result = hugepage_vma_revalidate(mm, addr, false, &vma, > > cc); > > if (result != SCAN_SUCCEED) { > > @@ -2864,7 +2866,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, > > (in hurry so I might be wrong) > > Do we have to handle when collapse_single_pmd() dropped the lock as well? That updates mmap_unlocked which will be handled in the loop or on exit: if (mmap_unlocked) { ... mmap_read_lock(mm); mmap_unlocked = false; *lock_dropped = true; ... } result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc); ... out_maybelock: /* Caller expects us to hold mmap_lock on return */ if (mmap_unlocked) { *lock_dropped = true; mmap_read_lock(mm); } > > -- > Cheers, > > David Thanks, Lorenzo