From 97769a53f117e2f33864c587d85992ee35194ecf Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Fri, 21 Feb 2025 18:44:23 -0800 Subject: mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation Tracing BPF programs execute from tracepoints and kprobes where running context is unknown, but they need to request additional memory. The prior workarounds were using pre-allocated memory and BPF specific freelists to satisfy such allocation requests. Instead, introduce gfpflags_allow_spinning() condition that signals to the allocator that running context is unknown. Then rely on percpu free list of pages to allocate a page. try_alloc_pages() -> get_page_from_freelist() -> rmqueue() -> rmqueue_pcplist() will spin_trylock to grab the page from percpu free list. If it fails (due to re-entrancy or list being empty) then rmqueue_bulk()/rmqueue_buddy() will attempt to spin_trylock zone->lock and grab the page from there. spin_trylock() is not safe in PREEMPT_RT when in NMI or in hard IRQ. Bailout early in such case. The support for gfpflags_allow_spinning() mode for free_page and memcg comes in the next patches. This is a first step towards supporting BPF requirements in SLUB and getting rid of bpf_mem_alloc. That goal was discussed at LSFMM: https://lwn.net/Articles/974138/ Acked-by: Michal Hocko Acked-by: Vlastimil Babka Acked-by: Sebastian Andrzej Siewior Reviewed-by: Shakeel Butt Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/r/20250222024427.30294-3-alexei.starovoitov@gmail.com Signed-off-by: Alexei Starovoitov --- lib/stackdepot.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'lib') diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 245d5b416699..377194969e61 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -591,7 +591,8 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, depot_stack_handle_t handle = 0; struct page *page = NULL; void *prealloc = NULL; - bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC; + bool allow_spin = gfpflags_allow_spinning(alloc_flags); + bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin; unsigned long flags; u32 hash; @@ -630,7 +631,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, prealloc = page_address(page); } - if (in_nmi()) { + if (in_nmi() || !allow_spin) { /* We can never allocate in NMI context. */ WARN_ON_ONCE(can_alloc); /* Best effort; bail if we fail to take the lock. */ -- cgit v1.2.3 From 8c57b687e8331eb80e302a2c528b18b966a9ac7a Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Fri, 21 Feb 2025 18:44:24 -0800 Subject: mm, bpf: Introduce free_pages_nolock() Introduce free_pages_nolock() that can free pages without taking locks. It relies on trylock and can be called from any context. Since spin_trylock() cannot be used in PREEMPT_RT from hard IRQ or NMI it uses lockless link list to stash the pages which will be freed by subsequent free_pages() from good context. Do not use llist unconditionally. BPF maps continuously allocate/free, so we cannot unconditionally delay the freeing to llist. When the memory becomes free make it available to the kernel and BPF users right away if possible, and fallback to llist as the last resort. Acked-by: Vlastimil Babka Acked-by: Sebastian Andrzej Siewior Reviewed-by: Shakeel Butt Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/r/20250222024427.30294-4-alexei.starovoitov@gmail.com Signed-off-by: Alexei Starovoitov --- include/linux/gfp.h | 1 + include/linux/mm_types.h | 4 +++ include/linux/mmzone.h | 3 ++ lib/stackdepot.c | 5 ++- mm/page_alloc.c | 93 +++++++++++++++++++++++++++++++++++++++++------- mm/page_owner.c | 8 ++++- 6 files changed, 100 insertions(+), 14 deletions(-) (limited to 'lib') diff --git a/include/linux/gfp.h b/include/linux/gfp.h index 5d9ee78c74e4..ceb226c2e25c 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -379,6 +379,7 @@ __meminit void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mas __get_free_pages((gfp_mask) | GFP_DMA, (order)) extern void __free_pages(struct page *page, unsigned int order); +extern void free_pages_nolock(struct page *page, unsigned int order); extern void free_pages(unsigned long addr, unsigned int order); #define __free_page(page) __free_pages((page), 0) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 6b27db7f9496..483aa90242cd 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -99,6 +99,10 @@ struct page { /* Or, free page */ struct list_head buddy_list; struct list_head pcp_list; + struct { + struct llist_node pcp_llist; + unsigned int order; + }; }; /* See page-flags.h for PAGE_MAPPING_FLAGS */ struct address_space *mapping; diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 9540b41894da..e16939553930 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -972,6 +972,9 @@ struct zone { /* Primarily protects free_area */ spinlock_t lock; + /* Pages to be freed when next trylock succeeds */ + struct llist_head trylock_free_pages; + /* Write-intensive fields used by compaction and vmstats. */ CACHELINE_PADDING(_pad2_); diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 377194969e61..73d7b50924ef 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -672,7 +672,10 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, exit: if (prealloc) { /* Stack depot didn't use this memory, free it. */ - free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); + if (!allow_spin) + free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER); + else + free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); } if (found) handle = found->handle.handle; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 99753bb9d707..52836eb65032 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -88,6 +88,9 @@ typedef int __bitwise fpi_t; */ #define FPI_TO_TAIL ((__force fpi_t)BIT(1)) +/* Free the page without taking locks. Rely on trylock only. */ +#define FPI_TRYLOCK ((__force fpi_t)BIT(2)) + /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */ static DEFINE_MUTEX(pcp_batch_high_lock); #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8) @@ -1249,13 +1252,44 @@ static void split_large_buddy(struct zone *zone, struct page *page, } while (1); } +static void add_page_to_zone_llist(struct zone *zone, struct page *page, + unsigned int order) +{ + /* Remember the order */ + page->order = order; + /* Add the page to the free list */ + llist_add(&page->pcp_llist, &zone->trylock_free_pages); +} + static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn, unsigned int order, fpi_t fpi_flags) { + struct llist_head *llhead; unsigned long flags; - spin_lock_irqsave(&zone->lock, flags); + if (!spin_trylock_irqsave(&zone->lock, flags)) { + if (unlikely(fpi_flags & FPI_TRYLOCK)) { + add_page_to_zone_llist(zone, page, order); + return; + } + spin_lock_irqsave(&zone->lock, flags); + } + + /* The lock succeeded. Process deferred pages. */ + llhead = &zone->trylock_free_pages; + if (unlikely(!llist_empty(llhead) && !(fpi_flags & FPI_TRYLOCK))) { + struct llist_node *llnode; + struct page *p, *tmp; + + llnode = llist_del_all(llhead); + llist_for_each_entry_safe(p, tmp, llnode, pcp_llist) { + unsigned int p_order = p->order; + + split_large_buddy(zone, p, page_to_pfn(p), p_order, fpi_flags); + __count_vm_events(PGFREE, 1 << p_order); + } + } split_large_buddy(zone, page, pfn, order, fpi_flags); spin_unlock_irqrestore(&zone->lock, flags); @@ -2599,7 +2633,7 @@ static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone, static void free_frozen_page_commit(struct zone *zone, struct per_cpu_pages *pcp, struct page *page, int migratetype, - unsigned int order) + unsigned int order, fpi_t fpi_flags) { int high, batch; int pindex; @@ -2634,6 +2668,14 @@ static void free_frozen_page_commit(struct zone *zone, } if (pcp->free_count < (batch << CONFIG_PCP_BATCH_SCALE_MAX)) pcp->free_count += (1 << order); + + if (unlikely(fpi_flags & FPI_TRYLOCK)) { + /* + * Do not attempt to take a zone lock. Let pcp->count get + * over high mark temporarily. + */ + return; + } high = nr_pcp_high(pcp, zone, batch, free_high); if (pcp->count >= high) { free_pcppages_bulk(zone, nr_pcp_free(pcp, batch, high, free_high), @@ -2648,7 +2690,8 @@ static void free_frozen_page_commit(struct zone *zone, /* * Free a pcp page */ -void free_frozen_pages(struct page *page, unsigned int order) +static void __free_frozen_pages(struct page *page, unsigned int order, + fpi_t fpi_flags) { unsigned long __maybe_unused UP_flags; struct per_cpu_pages *pcp; @@ -2657,7 +2700,7 @@ void free_frozen_pages(struct page *page, unsigned int order) int migratetype; if (!pcp_allowed_order(order)) { - __free_pages_ok(page, order, FPI_NONE); + __free_pages_ok(page, order, fpi_flags); return; } @@ -2675,23 +2718,33 @@ void free_frozen_pages(struct page *page, unsigned int order) migratetype = get_pfnblock_migratetype(page, pfn); if (unlikely(migratetype >= MIGRATE_PCPTYPES)) { if (unlikely(is_migrate_isolate(migratetype))) { - free_one_page(zone, page, pfn, order, FPI_NONE); + free_one_page(zone, page, pfn, order, fpi_flags); return; } migratetype = MIGRATE_MOVABLE; } + if (unlikely((fpi_flags & FPI_TRYLOCK) && IS_ENABLED(CONFIG_PREEMPT_RT) + && (in_nmi() || in_hardirq()))) { + add_page_to_zone_llist(zone, page, order); + return; + } pcp_trylock_prepare(UP_flags); pcp = pcp_spin_trylock(zone->per_cpu_pageset); if (pcp) { - free_frozen_page_commit(zone, pcp, page, migratetype, order); + free_frozen_page_commit(zone, pcp, page, migratetype, order, fpi_flags); pcp_spin_unlock(pcp); } else { - free_one_page(zone, page, pfn, order, FPI_NONE); + free_one_page(zone, page, pfn, order, fpi_flags); } pcp_trylock_finish(UP_flags); } +void free_frozen_pages(struct page *page, unsigned int order) +{ + __free_frozen_pages(page, order, FPI_NONE); +} + /* * Free a batch of folios */ @@ -2780,7 +2833,7 @@ void free_unref_folios(struct folio_batch *folios) trace_mm_page_free_batched(&folio->page); free_frozen_page_commit(zone, pcp, &folio->page, migratetype, - order); + order, FPI_NONE); } if (pcp) { @@ -4822,9 +4875,10 @@ unsigned long get_zeroed_page_noprof(gfp_t gfp_mask) EXPORT_SYMBOL(get_zeroed_page_noprof); /** - * __free_pages - Free pages allocated with alloc_pages(). + * ___free_pages - Free pages allocated with alloc_pages(). * @page: The page pointer returned from alloc_pages(). * @order: The order of the allocation. + * @fpi_flags: Free Page Internal flags. * * This function can free multi-page allocations that are not compound * pages. It does not check that the @order passed in matches that of @@ -4841,22 +4895,37 @@ EXPORT_SYMBOL(get_zeroed_page_noprof); * Context: May be called in interrupt context or while holding a normal * spinlock, but not in NMI context or while holding a raw spinlock. */ -void __free_pages(struct page *page, unsigned int order) +static void ___free_pages(struct page *page, unsigned int order, + fpi_t fpi_flags) { /* get PageHead before we drop reference */ int head = PageHead(page); struct alloc_tag *tag = pgalloc_tag_get(page); if (put_page_testzero(page)) - free_frozen_pages(page, order); + __free_frozen_pages(page, order, fpi_flags); else if (!head) { pgalloc_tag_sub_pages(tag, (1 << order) - 1); while (order-- > 0) - free_frozen_pages(page + (1 << order), order); + __free_frozen_pages(page + (1 << order), order, + fpi_flags); } } +void __free_pages(struct page *page, unsigned int order) +{ + ___free_pages(page, order, FPI_NONE); +} EXPORT_SYMBOL(__free_pages); +/* + * Can be called while holding raw_spin_lock or from IRQ and NMI for any + * page type (not only those that came from try_alloc_pages) + */ +void free_pages_nolock(struct page *page, unsigned int order) +{ + ___free_pages(page, order, FPI_TRYLOCK); +} + void free_pages(unsigned long addr, unsigned int order) { if (addr != 0) { diff --git a/mm/page_owner.c b/mm/page_owner.c index 2d6360eaccbb..90e31d0e3ed7 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -294,7 +294,13 @@ void __reset_page_owner(struct page *page, unsigned short order) page_owner = get_page_owner(page_ext); alloc_handle = page_owner->handle; - handle = save_stack(GFP_NOWAIT | __GFP_NOWARN); + /* + * Do not specify GFP_NOWAIT to make gfpflags_allow_spinning() == false + * to prevent issues in stack_depot_save(). + * This is similar to try_alloc_pages() gfp flags, but only used + * to signal stack_depot to avoid spin_locks. + */ + handle = save_stack(__GFP_NOWARN); __update_page_owner_free_handle(page_ext, handle, order, current->pid, current->tgid, free_ts_nsec); page_ext_put(page_ext); -- cgit v1.2.3