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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1775031289; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=/GktzSnMJl8Ijyyr3l1owjiRLvmZas5MqD4wkLR/ZTI=; b=N9dyrhzOh+eyyAdJkvA0htj1aIlrxuRTTZNzRavUPe4J4+89bAbdwCcxpp+4euZnGL9lXM 6L/wWOs3l6MSFUMa+U1ShnL9p0dUID2BlcuIr8HIJjVESn6fTVHvWADlNlL2eiLm7veQQI 7QG2jRGA+k9ep/FVYat/JoW+524shrY= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id B9EFA600AD; Wed, 1 Apr 2026 08:14:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E7E4C4CEF7; Wed, 1 Apr 2026 08:14:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775031288; bh=iQ8EvU3tv/4pbsm6CfejJfK6S/sdYvvsil2MY6ruHb4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=urrgNB4v0h8P+iqymJ0YNB/+FOuzKEHPJOFOhpxTBlP48HAYopSHr9sh4n8Tkb5rk deGiFiB/CP54/VZ8aHeVfkDp94GgVjaxW0falDt7bA+7b7tg6R/C9sLuwx5P2+ThSF mxqah6eI+pjxCO+jEUHG9gQ+qe7uBwrxixxjc+qfod3tZezhS4QtvaxODbZ4Nm+7pa wTv4z1OFfVdx9lyGj8u/UIUnbzxw7RDm+djdReNBr9fkrPwC4k9kbP6D4cMGSI8gEw npH0PSYoPcoAAp8RRv0ITWaMMXpF+kq9SvpQ70UVYCVSelRWGkj0AJBhU3V5/ixZkR R+ynnXZubZ8AQ== Date: Wed, 1 Apr 2026 09:14:35 +0100 From: "Lorenzo Stoakes (Oracle)" To: Nico Pache Cc: "David Hildenbrand (Arm)" , 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: <87b83f7b-f0b1-4184-93a0-3b4b574c813b@lucifer.local> 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> <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> <440d6b8a-d299-43eb-83b5-6625f9468e5e@lucifer.local> <37132e09-9c03-4afc-bc73-4bca416c5343@kernel.org> <9d5a4703-a15e-4be6-926b-af2d98db40c0@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: m7bhyizixr8qio3dg1qguaygs7iqncqr X-Rspamd-Queue-Id: B8F8440009 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1775031289-201756 X-HE-Meta: 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 1IETYLAr DRTKTDfw5LLCYxqJjSEWmp3xgIBmTrVeSAzpCz5nqOTZ2xTe0zk6x1VXXYFWVFqJ9mgM2enN1ufGVaJZXtTICo2j2gOte70ctvXmk91hbxtnighpT6mchcfhUdWP52sp5cPRUHirXMkR6PHodpIjvtg4nWK0nrjEMjJ6usdOy7Wku6SYfp6NEtYUQN3jnSudQdtAy+lR0mL27SWooxkDMkWj3EXiSzHzQjk98kkrqnnrydzpXiqYuuoumd3caa2WtSMIYMpNFPrhRRx16biRlZ4Q9WyWiZPQo7qbSaXGp9ONW8hjrMSX85eMWN1+Vml2ZwIll7um03VizCU58upb9awlGnwAuyc4ovuIxnFq+M4GzXs/KNofdEzAzAA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 31, 2026 at 03:09:08PM -0600, Nico Pache wrote: > On Tue, Mar 31, 2026 at 3:04 PM David Hildenbrand (Arm) > wrote: > > > > On 3/31/26 22:50, David Hildenbrand (Arm) wrote: > > > On 3/31/26 22:06, Lorenzo Stoakes (Oracle) wrote: > > >> On Tue, Mar 31, 2026 at 10:00:58PM +0200, David Hildenbrand (Arm) wrote: > > >>> > > >>> Right. > > >>> > > >>> The original code used > > >>> > > >>> bool mmap_locked = true; > > >>> > > >>> If the fix get squashed, maybe we should revert to that handling to > > >>> minimize the churn? > > >> > > >> Well collapse_single_pmd() and all descendents would need to be updated to > > >> invert the boolean, not sure it's worth it. > > > > > > The code is confusing me. > > > > > > In the old code, collapse_single_pmd() was called with "mmap_locked == > > > true" and set "mmap_locked=false". > > > > > > Now we call it with "mmap_unlocked=false" and it sets "mmap_unlocked=true". > > > > > > So far so good. > > > > > > However, collapse_scan_pmd() consumed "mmap_locked", now it effectively > > > consumes "mmap_unlocked". > > > > Okay, I'm too confused for today and give up :) > > > > FWIW, this is the effective change, and the effective changes to > > mmap_unlocked and lock_dropped ... confuse me: > > basically all the logic was inverted. Yup. > > out_maybelock: > > /* Caller expects us to hold mmap_lock on return */ > > - if (!mmap_locked) > > + if (mmap_unlocked) { > > + *lock_dropped = false; > > Lorenzo, is this correct? At first glance, shouldn't this be > `locked_dropped = true`? It is :) you're looking at the old code from your patch maybe? I include my fix-patch again below to make life easier, but that code is: + if (mmap_unlocked) { cond_resched(); mmap_read_lock(mm); - *lock_dropped = false; + mmap_unlocked = false; + *lock_dropped = true; Having one on top of the other is causing the confusion :) I also asked Claude to check this btw for correctness. I'm pretty confident it's ok. Cheers, Lorenzo ----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, hend = min(hend, vma->vm_end & HPAGE_PMD_MASK); } - result = collapse_single_pmd(addr, vma, lock_dropped, cc); + result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc); switch (result) { case SCAN_SUCCEED: @@ -2893,8 +2895,10 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, out_maybelock: /* Caller expects us to hold mmap_lock on return */ - if (*lock_dropped) + if (mmap_unlocked) { + *lock_dropped = true; mmap_read_lock(mm); + } out_nolock: mmap_assert_locked(mm); mmdrop(mm); -- 2.53.0