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Fri, 30 May 2025 10:39:42 +0800 Message-ID: Date: Fri, 30 May 2025 10:39:41 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm: shmem: disallow hugepages if the system-wide shmem THP sysfs settings are disabled To: Zi Yan Cc: akpm@linux-foundation.org, hughd@google.com, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <6132583a-1754-4eb1-9b84-19b55cac176c@linux.alibaba.com> <548AFF46-93AF-40CB-80E4-372DAAA9F80B@nvidia.com> From: Baolin Wang In-Reply-To: <548AFF46-93AF-40CB-80E4-372DAAA9F80B@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: 8kqmee9z47rxkq9zsuhes9bq9o154h9y X-Rspamd-Queue-Id: E170620002 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1748572786-690822 X-HE-Meta: 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 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: On 2025/5/30 10:35, Zi Yan wrote: > On 29 May 2025, at 22:32, Baolin Wang wrote: > >> On 2025/5/30 10:17, Zi Yan wrote: >>> On 29 May 2025, at 21:58, Baolin Wang wrote: >>> >>>> On 2025/5/29 23:21, Zi Yan wrote: >>>>> On 29 May 2025, at 4:23, Baolin Wang wrote: >>>>> >>>>>> The MADV_COLLAPSE will ignore the system-wide shmem THP sysfs settings, which >>>>>> means that even though we have disabled the shmem THP configuration, MADV_COLLAPSE >>>>>> will still attempt to collapse into a shmem THP. This violates the rule we have >>>>>> agreed upon: never means never. >>>>>> >>>>>> Then the current strategy is: >>>>>> For shmem, if none of always, madvise, within_size, and inherit have enabled >>>>>> PMD-sized mTHP, then MADV_COLLAPSE will be prohibited from collapsing PMD-sized mTHP. >>>>>> >>>>>> For tmpfs, if the mount option is set with the 'huge=never' parameter, then >>>>>> MADV_COLLAPSE will be prohibited from collapsing PMD-sized mTHP. >>>>>> >>>>>> Signed-off-by: Baolin Wang >>>>>> --- >>>>>> mm/huge_memory.c | 2 +- >>>>>> mm/shmem.c | 12 ++++++------ >>>>>> 2 files changed, 7 insertions(+), 7 deletions(-) >>>>>> >>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>>>> index d3e66136e41a..a8cfa37cae72 100644 >>>>>> --- a/mm/huge_memory.c >>>>>> +++ b/mm/huge_memory.c >>>>>> @@ -166,7 +166,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, >>>>>> * own flags. >>>>>> */ >>>>>> if (!in_pf && shmem_file(vma->vm_file)) >>>>>> - return shmem_allowable_huge_orders(file_inode(vma->vm_file), >>>>>> + return orders & shmem_allowable_huge_orders(file_inode(vma->vm_file), >>>>>> vma, vma->vm_pgoff, 0, >>>>>> !enforce_sysfs); >>>>> >>>>> OK, here orders is checked against allowed orders. >>>>> >>>>>> >>>>>> diff --git a/mm/shmem.c b/mm/shmem.c >>>>>> index 4b42419ce6b2..4dbb28d85cd9 100644 >>>>>> --- a/mm/shmem.c >>>>>> +++ b/mm/shmem.c >>>>>> @@ -613,7 +613,7 @@ static unsigned int shmem_get_orders_within_size(struct inode *inode, >>>>>> } >>>>>> >>>>>> static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index, >>>>>> - loff_t write_end, bool shmem_huge_force, >>>>>> + loff_t write_end, >>>>>> struct vm_area_struct *vma, >>>>>> unsigned long vm_flags) >>>>>> { >>>>>> @@ -625,7 +625,7 @@ static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index >>>>>> return 0; >>>>>> if (shmem_huge == SHMEM_HUGE_DENY) >>>>>> return 0; >>>>>> - if (shmem_huge_force || shmem_huge == SHMEM_HUGE_FORCE) >>>>>> + if (shmem_huge == SHMEM_HUGE_FORCE) >>>>>> return maybe_pmd_order; >>>>> >>>>> shmem_huge is set by sysfs? >>>> >>>> Yes, through the '/sys/kernel/mm/transparent_hugepage/shmem_enabled' interface. >>>> >>>>>> /* >>>>>> @@ -860,7 +860,7 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, >>>>>> } >>>>>> >>>>>> static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index, >>>>>> - loff_t write_end, bool shmem_huge_force, >>>>>> + loff_t write_end, >>>>>> struct vm_area_struct *vma, >>>>>> unsigned long vm_flags) >>>>>> { >>>>>> @@ -1261,7 +1261,7 @@ static int shmem_getattr(struct mnt_idmap *idmap, >>>>>> STATX_ATTR_NODUMP); >>>>>> generic_fillattr(idmap, request_mask, inode, stat); >>>>>> >>>>>> - if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0)) >>>>>> + if (shmem_huge_global_enabled(inode, 0, 0, NULL, 0)) >>>>>> stat->blksize = HPAGE_PMD_SIZE; >>>>>> >>>>>> if (request_mask & STATX_BTIME) { >>>>>> @@ -1768,7 +1768,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, >>>>>> return 0; >>>>>> >>>>>> global_orders = shmem_huge_global_enabled(inode, index, write_end, >>>>>> - shmem_huge_force, vma, vm_flags); >>>>>> + vma, vm_flags); >>>>>> /* Tmpfs huge pages allocation */ >>>>>> if (!vma || !vma_is_anon_shmem(vma)) >>>>>> return global_orders; >>>>>> @@ -1790,7 +1790,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, >>>>>> /* Allow mTHP that will be fully within i_size. */ >>>>>> mask |= shmem_get_orders_within_size(inode, within_size_orders, index, 0); >>>>>> >>>>>> - if (vm_flags & VM_HUGEPAGE) >>>>>> + if (shmem_huge_force || (vm_flags & VM_HUGEPAGE)) >>>>>> mask |= READ_ONCE(huge_shmem_orders_madvise); >>>>>> >>>>>> if (global_orders > 0) >>>>>> -- >>>>>> 2.43.5 >>>>> >>>>> shmem_huge_force comes from !enforce_sysfs in __thp_vma_allowable_orders(). >>>>> Do you know when sysfs is not enforced and why? >>>> >>>> IIUC, shmem_huge_force will only be set during MADV_COLLAPSE. Originally, MADV_COLLAPSE was intended to ignore the system-wide THP sysfs settings. However, if all system-wide shmem THP settings are disabled, we should not allow MADV_COLLAPSE to collapse a THP. This is the issue this patchset aims to fix. Thanks for the review. >>> >>> Got it. If we want to enforce sysfs, why not just get rid of TVA_ENFORCE_SYSFS >>> and make everyone follow sysfs? >> >> Now MADV_COLLAPSE will ignore the VM_HUGEPAGE, while the others will check the VM_HUGEPAGE flag before using 'huge_shmem_orders_madvise' with the TVA_ENFORCE_SYSFS flag set. >> >> That is to follow the rule: “allowing for collapsing in a VM without VM_HUGEPAGE in the "madvise" mode would be fine". > > Can you add this rule in your commit message? It clarifies things. Sure. Will do. >> So I think we should still keep the TVA_ENFORCE_SYSFS flag. > > Got it. Thank you for the explanation. > > Acked-by: Zi Yan Thanks for reviewing.