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b=GkDOVQGijiYAfBZ5fT2rU6iC7mMAnJF3Zg3lk1KrOMYnGUQTpiLp1pq6d3jHY9B7M ky/yN5Ky10qZVy68U98IDwjnlIClc8iwGBHIfrJ+b9XGUrE0bQDspTML5gdDm7Hs5T LOdelE40N+ln0/eh5sq3RfiUz6UGtfEp/kLV/8pP7HwXpWmVj54KXHzf+03HcfXHSa gV2YOIKV0S7/itS3irmnD32F8P4VNxgsug8YiS1R3NPov/aoLN7JCrU0AXfSgubkVZ D28OqAdbTskExpirD5MRyG3NZDC8cYvq5ARxMXYKkAU+mGJS7/l90ISH/zzZk5RU36 gYBUWcRi3aD5g== Date: Tue, 31 Mar 2026 21:06:30 +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: <440d6b8a-d299-43eb-83b5-6625f9468e5e@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> X-Rspamd-Queue-Id: E1EC44000B X-Stat-Signature: e1h9px8qycsbpnao68qi96ynrcezcngz X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1774987604-126257 X-HE-Meta: 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 6OPBvKiG vQf0g8ohAHmWSZbB1XsEjKqoCbhBbCyk/8V896aUN58aKuteNil7y5jvHBqzzr0BPDC0zKc3xt0gsGN8n5qZteqgGzDGyaAUVGQY7pFnGV++cgcXg6tSBvvA3APsS+kdaa2O8PlgFeKzqlfH2oSczp7I84r1qi43l08ueoChGLS8yKUtKVXOzT0Py+nYBbMxF+k4IWUWdIdpGTxgmn4/55PoVO0HVatUhmIV94taphnMVEUQZxAgQnvlSnvl30lKr5qdp7Htn3vvwx3Ob7r0lyqFdbMTS04PA+t5L3uHR6EYHkKdX0i3V6OAE4yCd2JhEipjMvtOtf15/Er0QtQDdzFEOMh9PsEnqS+7O 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 10:00:58PM +0200, David Hildenbrand (Arm) wrote: > On 3/31/26 16:15, Lorenzo Stoakes (Oracle) wrote: > > On Tue, Mar 31, 2026 at 04:13:29PM +0200, David Hildenbrand (Arm) wrote: > >>> > >>> 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); > > } > > > > 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. > > (this is not in stable, right?) > > -- > Cheers, > > David