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Thu, 15 Jan 2026 18:00:37 +0800 Message-ID: <0bc3807e-2c1b-43af-9aab-665ce30d49d4@linux.alibaba.com> Date: Thu, 15 Jan 2026 18:00:36 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/1] mm/khugepaged: move tlb_remove_table_sync_one out from under PTL To: Lance Yang , akpm@linux-foundation.org, david@kernel.org Cc: ioworker0@gmail.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260115071651.42626-1-lance.yang@linux.dev> From: Baolin Wang In-Reply-To: <20260115071651.42626-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: rokh8s3m7b9ke7gjcbzuyonszo3z56my X-Rspam-User: X-Rspamd-Queue-Id: 9CF13140011 X-Rspamd-Server: rspam08 X-HE-Tag: 1768471244-569921 X-HE-Meta: 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 EfGeQBr3 kl7GODNe7sq34lbDFLnUo0V1aI3Rb+XUZWJvONOY+nAcFKUin7TZmg80WHij9xtgmTW691huxVcNIh4FiJNjRMA4qbg/M+9XI138IRLBcYF56H7RHtBRNaFcrfWnX/5hHH/5vKnUaSA/RwHDV13p/eYN6zAoKs0oMdqVGJUZ9up1D97EkZ7LhIired3fsN81rc437Lx/zwETuEXvcKBsCI1Guh9pF+DuCDALo/hgItwWkg1B9eb79U2aB19hYwuSje3z69MrN0guecXGI+iYJGU+p3Zti20mcXGHUMLclVn74xqCtm7Im+zEWZB0oCzaJ09RVJV88+Cd8BR/K5k+zDEsghUu5HbLuR1qQ7JrWP4jXh3/TJvpMEyW1HQA4+Q/zvcWE+iKp0uKkB6k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Lance, On 1/15/26 3:16 PM, Lance Yang wrote: > From: Lance Yang > > tlb_remove_table_sync_one() sends IPIs to all CPUs and waits for them, > which we really don't want to do while holding PTL. Could you add more comments to explain why this is safe for the PAE case? For the non-PAE case, you added a new tlb_remove_table_sync_one(), why we need this (to solve what problem)? Please also add more comments to explain. > Just move the call to after we release PTL, and drop the macro wrapper > while we're at it. > > Signed-off-by: Lance Yang > --- > include/linux/pgtable.h | 4 ---- > mm/khugepaged.c | 5 +++-- > 2 files changed, 3 insertions(+), 6 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index eb8aacba3698..fb04ed22052c 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -755,7 +755,6 @@ static inline pmd_t pmdp_get_lockless(pmd_t *pmdp) > return pmd; > } > #define pmdp_get_lockless pmdp_get_lockless > -#define pmdp_get_lockless_sync() tlb_remove_table_sync_one() > #endif /* CONFIG_PGTABLE_LEVELS > 2 */ > #endif /* CONFIG_GUP_GET_PXX_LOW_HIGH */ > > @@ -774,9 +773,6 @@ static inline pmd_t pmdp_get_lockless(pmd_t *pmdp) > { > return pmdp_get(pmdp); > } > -static inline void pmdp_get_lockless_sync(void) > -{ > -} > #endif > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 9f790ec34400..0a6cebf880e0 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1664,10 +1664,10 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign > } > } > pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd); > - pmdp_get_lockless_sync(); > pte_unmap_unlock(start_pte, ptl); > if (ptl != pml) > spin_unlock(pml); > + tlb_remove_table_sync_one(); > > mmu_notifier_invalidate_range_end(&range); > > @@ -1818,7 +1818,6 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > */ > if (likely(file_backed_vma_is_retractable(vma))) { > pgt_pmd = pmdp_collapse_flush(vma, addr, pmd); > - pmdp_get_lockless_sync(); > success = true; > } > > @@ -1826,6 +1825,8 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > spin_unlock(ptl); > drop_pml: > spin_unlock(pml); > + if (success) > + tlb_remove_table_sync_one(); > > mmu_notifier_invalidate_range_end(&range); >