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owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Sep 12, 2025 at 04:28:46PM +0800, Yafang Shao wrote: > On Thu, Sep 11, 2025 at 10:34 PM Lorenzo Stoakes > wrote: > > > > On Wed, Sep 10, 2025 at 10:44:39AM +0800, Yafang Shao wrote: > > > This patch introduces a new BPF struct_ops called bpf_thp_ops for dynamic > > > THP tuning. It includes a hook bpf_hook_thp_get_order(), allowing BPF > > > programs to influence THP order selection based on factors such as: > > > - Workload identity > > > For example, workloads running in specific containers or cgroups. > > > - Allocation context > > > Whether the allocation occurs during a page fault, khugepaged, swap or > > > other paths. > > > - VMA's memory advice settings > > > MADV_HUGEPAGE or MADV_NOHUGEPAGE > > > - Memory pressure > > > PSI system data or associated cgroup PSI metrics > > > > > > The kernel API of this new BPF hook is as follows, > > > > > > /** > > > * @thp_order_fn_t: Get the suggested THP orders from a BPF program for allocation > > > * @vma: vm_area_struct associated with the THP allocation > > > * @vma_type: The VMA type, such as BPF_THP_VM_HUGEPAGE if VM_HUGEPAGE is set > > > * BPF_THP_VM_NOHUGEPAGE if VM_NOHUGEPAGE is set, or BPF_THP_VM_NONE if > > > * neither is set. > > > * @tva_type: TVA type for current @vma > > > * @orders: Bitmask of requested THP orders for this allocation > > > * - PMD-mapped allocation if PMD_ORDER is set > > > * - mTHP allocation otherwise > > > * > > > * Return: The suggested THP order from the BPF program for allocation. It will > > > * not exceed the highest requested order in @orders. Return -1 to > > > * indicate that the original requested @orders should remain unchanged. > > > */ > > > typedef int thp_order_fn_t(struct vm_area_struct *vma, > > > enum bpf_thp_vma_type vma_type, > > > enum tva_type tva_type, > > > unsigned long orders); > > > > > > Only a single BPF program can be attached at any given time, though it can > > > be dynamically updated to adjust the policy. The implementation supports > > > anonymous THP, shmem THP, and mTHP, with future extensions planned for > > > file-backed THP. > > > > > > This functionality is only active when system-wide THP is configured to > > > madvise or always mode. It remains disabled in never mode. Additionally, > > > if THP is explicitly disabled for a specific task via prctl(), this BPF > > > functionality will also be unavailable for that task. > > > > > > This feature requires CONFIG_BPF_GET_THP_ORDER (marked EXPERIMENTAL) to be > > > enabled. Note that this capability is currently unstable and may undergo > > > significant changes—including potential removal—in future kernel versions. > > > > Thanks for highlighting. > > > > > > > > Suggested-by: David Hildenbrand > > > Suggested-by: Lorenzo Stoakes > > > Signed-off-by: Yafang Shao > > > --- > > > MAINTAINERS | 1 + > > > include/linux/huge_mm.h | 26 ++++- > > > mm/Kconfig | 12 ++ > > > mm/Makefile | 1 + > > > mm/huge_memory_bpf.c | 243 ++++++++++++++++++++++++++++++++++++++++ > > > 5 files changed, 280 insertions(+), 3 deletions(-) > > > create mode 100644 mm/huge_memory_bpf.c > > > > > > diff --git a/MAINTAINERS b/MAINTAINERS > > > index 8fef05bc2224..d055a3c95300 100644 > > > --- a/MAINTAINERS > > > +++ b/MAINTAINERS > > > @@ -16252,6 +16252,7 @@ F: include/linux/huge_mm.h > > > F: include/linux/khugepaged.h > > > F: include/trace/events/huge_memory.h > > > F: mm/huge_memory.c > > > +F: mm/huge_memory_bpf.c > > > > THanks! > > > > > F: mm/khugepaged.c > > > F: mm/mm_slot.h > > > F: tools/testing/selftests/mm/khugepaged.c > > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > > > index 23f124493c47..f72a5fd04e4f 100644 > > > --- a/include/linux/huge_mm.h > > > +++ b/include/linux/huge_mm.h > > > @@ -56,6 +56,7 @@ enum transparent_hugepage_flag { > > > TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, > > > TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG, > > > TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG, > > > + TRANSPARENT_HUGEPAGE_BPF_ATTACHED, /* BPF prog is attached */ > > > }; > > > > > > struct kobject; > > > @@ -270,6 +271,19 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > > > enum tva_type type, > > > unsigned long orders); > > > > > > +#ifdef CONFIG_BPF_GET_THP_ORDER > > > +unsigned long > > > +bpf_hook_thp_get_orders(struct vm_area_struct *vma, vm_flags_t vma_flags, > > > + enum tva_type type, unsigned long orders); > > > > Thanks for renaming! > > > > > +#else > > > +static inline unsigned long > > > +bpf_hook_thp_get_orders(struct vm_area_struct *vma, vm_flags_t vma_flags, > > > + enum tva_type tva_flags, unsigned long orders) > > > +{ > > > + return orders; > > > +} > > > +#endif > > > + > > > /** > > > * thp_vma_allowable_orders - determine hugepage orders that are allowed for vma > > > * @vma: the vm area to check > > > @@ -291,6 +305,12 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma, > > > enum tva_type type, > > > unsigned long orders) > > > { > > > + unsigned long bpf_orders; > > > + > > > + bpf_orders = bpf_hook_thp_get_orders(vma, vm_flags, type, orders); > > > + if (!bpf_orders) > > > + return 0; > > > > I think it'd be easier to just do: > > > > /* The BPF-specified order overrides which order is selected. */ > > orders &= bpf_hook_thp_get_orders(vma, vm_flags, type, orders); > > if (!orders) > > return 0; > > good suggestion! Thanks, though this does come back to 'are we masking on orders' or not. Obviously this is predicated on that being the case. > > > struct thpsize { > > > diff --git a/mm/Kconfig b/mm/Kconfig > > > index d1ed839ca710..4d89d2158f10 100644 > > > --- a/mm/Kconfig > > > +++ b/mm/Kconfig > > > @@ -896,6 +896,18 @@ config NO_PAGE_MAPCOUNT > > > > > > EXPERIMENTAL because the impact of some changes is still unclear. > > > > > > +config BPF_GET_THP_ORDER > > > > Yeah, I think we maybe need to sledgehammer this as already Lance was confused > > as to the permenancy of this, and I feel that users might be too, even with the > > '(EXPERIMENTAL)' bit. > > > > So maybe > > > > config BPF_GET_THP_ORDER_EXPERIMENTAL > > > > Just to hammer it home? > > ack Thanks! > > > > > > + bool "BPF-based THP order selection (EXPERIMENTAL)" > > > + depends on TRANSPARENT_HUGEPAGE && BPF_SYSCALL > > > + > > > + help > > > + Enable dynamic THP order selection using BPF programs. This > > > + experimental feature allows custom BPF logic to determine optimal > > > + transparent hugepage allocation sizes at runtime. > > > + > > > + WARNING: This feature is unstable and may change in future kernel > > > + versions. > > > + > > > endif # TRANSPARENT_HUGEPAGE > > > > > > # simple helper to make the code a bit easier to read > > > diff --git a/mm/Makefile b/mm/Makefile > > > index 21abb3353550..f180332f2ad0 100644 > > > --- a/mm/Makefile > > > +++ b/mm/Makefile > > > @@ -99,6 +99,7 @@ obj-$(CONFIG_MIGRATION) += migrate.o > > > obj-$(CONFIG_NUMA) += memory-tiers.o > > > obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o > > > obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o > > > +obj-$(CONFIG_BPF_GET_THP_ORDER) += huge_memory_bpf.o > > > obj-$(CONFIG_PAGE_COUNTER) += page_counter.o > > > obj-$(CONFIG_MEMCG_V1) += memcontrol-v1.o > > > obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o > > > diff --git a/mm/huge_memory_bpf.c b/mm/huge_memory_bpf.c > > > new file mode 100644 > > > index 000000000000..525ee22ab598 > > > --- /dev/null > > > +++ b/mm/huge_memory_bpf.c > > > @@ -0,0 +1,243 @@ > > > +// SPDX-License-Identifier: GPL-2.0 > > > +/* > > > + * BPF-based THP policy management > > > + * > > > + * Author: Yafang Shao > > > + */ > > > + > > > +#include > > > +#include > > > +#include > > > +#include > > > + > > > +enum bpf_thp_vma_type { > > > + BPF_THP_VM_NONE = 0, > > > + BPF_THP_VM_HUGEPAGE, /* VM_HUGEPAGE */ > > > + BPF_THP_VM_NOHUGEPAGE, /* VM_NOHUGEPAGE */ > > > +}; > > > > I'm really not so sure how useful this is - can't a user just ascertain this > > from the VMA flags themselves? > > I assume you are referring to checking flags from vma->vm_flags. > There is an exception where we cannot use vma->vm_flags: in > hugepage_madvise(), which calls khugepaged_enter_vma(vma, *vm_flags). > > At this point, the VM_HUGEPAGE flag has not been set in vma->vm_flags > yet. Therefore, we must pass the separate *vm_flags variable. > Perhaps we can simplify the logic with the following change? Ugh god. I guess this is the workaround for the vm_flags thing right. > > diff --git a/mm/madvise.c b/mm/madvise.c > index 35ed4ab0d7c5..5755de80a4d7 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1425,6 +1425,8 @@ static int madvise_vma_behavior(struct > madvise_behavior *madv_behavior) > VM_WARN_ON_ONCE(madv_behavior->lock_mode != MADVISE_MMAP_WRITE_LOCK); > > error = madvise_update_vma(new_flags, madv_behavior); > + if (new_flags & VM_HUGEPAGE) > + khugepaged_enter_vma(vma); Hm ok, that's not such a bad idea, though ofc this should be something like: if (!error && (new_flags & VM_HUGEPAGE)) khugepaged_enter_vma(vma); And obviously dropping this khugepaged_enter_vma() from hugepage_madvise(). > out: > /* > * madvise() returns EAGAIN if kernel resources, such as > > > > > Let's keep the interface as minimal as possible. > > > > > + > > > +/** > > > + * @thp_order_fn_t: Get the suggested THP orders from a BPF program for allocation > > > > orders -> order? > > ack Thanks! > > > > > > + * @vma: vm_area_struct associated with the THP allocation > > > + * @vma_type: The VMA type, such as BPF_THP_VM_HUGEPAGE if VM_HUGEPAGE is set > > > + * BPF_THP_VM_NOHUGEPAGE if VM_NOHUGEPAGE is set, or BPF_THP_VM_NONE if > > > + * neither is set. > > > > Obv as above let's drop this probably :) > > > > > + * @tva_type: TVA type for current @vma > > > + * @orders: Bitmask of requested THP orders for this allocation > > > > Shouldn't requested = available? > > ack Thanks! > > > > > > + * - PMD-mapped allocation if PMD_ORDER is set > > > + * - mTHP allocation otherwise > > > > Not sure these 2 points are super useful. > > will remove it. Thanks! > > > > > > + * > > > + * Return: The suggested THP order from the BPF program for allocation. It will > > > + * not exceed the highest requested order in @orders. Return -1 to > > > + * indicate that the original requested @orders should remain unchanged. > > > + */ > > > +typedef int thp_order_fn_t(struct vm_area_struct *vma, > > > + enum bpf_thp_vma_type vma_type, > > > + enum tva_type tva_type, > > > + unsigned long orders); > > > + > > > +struct bpf_thp_ops { > > > + thp_order_fn_t __rcu *thp_get_order; > > > +}; > > > + > > > +static struct bpf_thp_ops bpf_thp; > > > +static DEFINE_SPINLOCK(thp_ops_lock); > > > + > > > +/* > > > + * Returns the original @orders if no BPF program is attached or if the > > > + * suggested order is invalid. > > > + */ > > > +unsigned long bpf_hook_thp_get_orders(struct vm_area_struct *vma, > > > + vm_flags_t vma_flags, > > > + enum tva_type tva_type, > > > + unsigned long orders) > > > +{ > > > + thp_order_fn_t *bpf_hook_thp_get_order; > > > + unsigned long thp_orders = orders; > > > + enum bpf_thp_vma_type vma_type; > > > + int thp_order; > > > + > > > + /* No BPF program is attached */ > > > + if (!test_bit(TRANSPARENT_HUGEPAGE_BPF_ATTACHED, > > > + &transparent_hugepage_flags)) > > > + return orders; > > > + > > > + if (vma_flags & VM_HUGEPAGE) > > > + vma_type = BPF_THP_VM_HUGEPAGE; > > > + else if (vma_flags & VM_NOHUGEPAGE) > > > + vma_type = BPF_THP_VM_NOHUGEPAGE; > > > + else > > > + vma_type = BPF_THP_VM_NONE; > > > > As per above, not sure this is all that useful. > > > > > + > > > + rcu_read_lock(); > > > + bpf_hook_thp_get_order = rcu_dereference(bpf_thp.thp_get_order); > > > + if (!bpf_hook_thp_get_order) > > > + goto out; > > > + > > > + thp_order = bpf_hook_thp_get_order(vma, vma_type, tva_type, orders); > > > + if (thp_order < 0) > > > + goto out; > > > + /* > > > + * The maximum requested order is determined by the callsite. E.g.: > > > + * - PMD-mapped THP uses PMD_ORDER > > > + * - mTHP uses (PMD_ORDER - 1) > > > > I don't think this is quite right, highest_order() figures out the highest set > > bit, so mTHP can be PMD_ORDER - 1 or less (in theory ofc). > > > > I think we can just replace this with something simpler like - 'depending on > > where the BPF hook is invoked, we check for either PMD order or mTHP orders > > (less than PMD order)' or something. > > ack Thanks! > > > > > > + * > > > + * We must respect this upper bound to avoid undefined behavior. So the > > > + * highest suggested order can't exceed the highest requested order. > > > + */ > > > > I think this sentence is also unnecessary. > > will remove it. Thanks! > > -- > Regards > Yafang Cheers, Lorenzo