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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774987275; bh=kuEwNYJuHC5gEhU4Iai/CMNylkeBV67na+CIWWZy6No=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=TdQhZogGxkhyUrr0rvgQYaHWDAY9Q7VMYbbQPkUz5koC6tSVAY3L72IGlMIPgYvo6 0hdshX27WRBpoluEOxy/Tx0NgDG97okbPAC424BFRM4/MroKRapiIZ6Tp/LVXsFDp5 XyN4JoAlxgkrXz2Yb3xH4CgOYLUbc9ToR0jDmmf46tGVswvN5UjD5Dyy+RRTBdb6A/ YuAlYOoCQUxezDcYdqfPkYInqCg3aYhz1XQK+PL9hLrTOymNvXpw/xwWEUu5kTip3X qIb/5c/3rPSB9oqB9Uv65FK0rUAHgku0i6WOP2ViR91X1oQk9Jirf+ui3a9lz3e6Zk qxUtvkvz0HmNQ== Message-ID: <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> Date: Tue, 31 Mar 2026 22:00:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v4 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() To: "Lorenzo Stoakes (Oracle)" 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 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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: xc7zdfpogzjaci7gqrt9sxtbp4r8bx4r X-Rspamd-Queue-Id: 3FD18140013 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774987277-967705 X-HE-Meta: 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 7POTuW8M EqaiK9L6XXpajRh0ZJeGbUEvC60jWeL+90LLNdlOMwpX0k+Hx2hXPzJW6Sf2gL7fjYtjFEJUdayBWk9LMq9Yb5PxOishK7YExJBfRAdo+OjlY5O0UT/F9odB3Q2dbYfb82hLVszDSWkKtn52XqjnP9Xf26zvOd8C2umkWBwIwVe+s5NUA6XMJRM7NWHTe6lUjvsQx4123j4vjwmuiYCv9vqfcU6SRzZ8fSsV5W+KEsIqUoH9hBccrz9il7fMXpz/ICJa9RcjJ6iE70pYlRxcFG1QU9Y7xqW/JuwemhHF75o+5ZEHGfqY+OhQ7lWtyonEiaGOsB173GcyVeSaUQ4b/FSdT1nqMAgjdJ2EAr8LOyM+q2Ui4kwmzV820yAT6nA+vudlhaddpt6/RlbPL/R1EeQv2kA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? (this is not in stable, right?) -- Cheers, David