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 <baolin.wang@xxxxxxxxxxxxxxxxx> --- 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) -- 2.43.5shmem_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.
