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Fri, 30 May 2025 10:32:25 +0800 Message-ID: <6132583a-1754-4eb1-9b84-19b55cac176c@linux.alibaba.com> Date: Fri, 30 May 2025 10:32:24 +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: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A01721C0004 X-Stat-Signature: drquddrpcxwggs17ubyjkphraw6rrd9p X-Rspam-User: X-HE-Tag: 1748572348-874203 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 10:17, 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". So I think we should still keep the TVA_ENFORCE_SYSFS flag.