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 imFpmx0H 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+0100, Lorenzo Stoakes wrote: > Not related to your patch at all, but man this whole thing (thp allowed orders) > needs significant improvement, it seems always perversely complicated for a > relatively simple operation. > > Overall I LOVE what you're doing here, but I feel we can clarify things a > little while we're at it to make it clear exactly what we're doing. > > This is a very important change so forgive my fiddling about here but I'm > hoping we can take the opportunity to make things a little simpler! > > On Thu, Jun 05, 2025 at 04:00:58PM +0800, Baolin Wang wrote: > > The MADV_COLLAPSE will ignore the system-wide Anon THP sysfs settings, which > > means that even though we have disabled the Anon THP configuration, MADV_COLLAPSE > > will still attempt to collapse into a Anon THP. This violates the rule we have > > agreed upon: never means never. > > > > Another rule for madvise, referring to David's suggestion: “allowing for collapsing > > in a VM without VM_HUGEPAGE in the "madvise" mode would be fine". > > I'm generally not sure it's worth talking only about MADV_COLLAPSE here when > you're changing what THP is permitted across the board, I may have missed some > discussion and forgive me if so, but what is special about MADV_COLLAPSE's use > of thp_vma_allowable_orders() that makes it ignore 'never's moreso than other > users? I'd mention that MADV_COLLAPSE is special because of not specifying TVA_ENFORCE_SYSFS but you are making this change across the board for all callers who do not specify this. I'd also CLEARLY mention that you handle David's request re: madvise by restricting yourself to checking only for NEVER and retaining the existing logic of not enforcing sysfs settings when TVA_ENFORCE_SYSFS, which includes not checking the VMA for VM_HUGEPAGE if the madvise mode is enabled. (i.e. addressing David's request). [snip] > I feel this is compressing a lot of logic in a way that took me several > readings to understand (hey I might not be the smartest cookie in the jar, > but we need to account for all levels of kernel developer ;) > > I feel like we can make things a lot clearer here by separating out with a > helper function (means we can drop some indentation too), and also take > advantage of the fact that, if orders == 0, __thp_vma_allowable_orders() > exits with 0 early so no need for us to do so ourselves: > > /* Strictly mask requested anonymous orders according to sysfs settings. */ > static inline unsigned long __thp_mask_anon_orders(unsigned long vm_flags, > unsigned long tva_flags, unsigned long orders) > { > unsigned long always = READ_ONCE(huge_anon_orders_always); > unsigned long madvise = READ_ONCE(huge_anon_orders_madvise); > unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);; > bool inherit_enabled = hugepage_global_enabled(); > bool has_madvise = vm_flags & VM_HUGEPAGE; > unsigned long mask = always | madvise; > > mask = always | madvise; > if (inherit_enabled) > mask |= inherit; > > /* All set to/inherit NEVER - never means never globally, abort. */ > if (!(mask & orders)) > return 0; > > /* Otherwise, we only enforce sysfs settings if asked. */ Perhaps worth adding a comment here noting that, if the user sets a sysfs mode of madvise and if TVA_ENFORCE_SYSFS is not set, we don't bother checking whether the VMA has VM_HUGEPAGE set. > if (!(tva_flags & TVA_ENFORCE_SYSFS)) > return orders; > > mask = always; > if (has_madvise) > mask |= madvise; > if (hugepage_global_always() || (has_madvise && inherit_enabled)) > mask |= inherit; > > return orders & mask; > } > > ... > > static inline > unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma, > unsigned long vm_flags, > unsigned long tva_flags, > unsigned long orders) > { > if (vma_is_anonymous(vma)) > orders = __thp_mask_anon_orders(vm_flags, tva_flags, orders); > > return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders); > } > > > > > -- > > 2.43.5 > >