From: Alexei Starovoitov <ast@xxxxxxxxxx> 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 internal __GFP_TRYLOCK flag that makes page allocator accessible from any context. It relies on percpu free list of pages that rmqueue_pcplist() should be able to pop the page from. If it fails (due to IRQ re-entrancy or list being empty) then try_alloc_pages() attempts to spin_trylock zone->lock and refill percpu freelist as normal. BPF program may execute with IRQs disabled and zone->lock is sleeping in RT, so trylock is the only option. In theory we can introduce percpu reentrance counter and increment it every time spin_lock_irqsave(&zone->lock, flags) is used, but we cannot rely on it. Even if this cpu is not in page_alloc path the spin_lock_irqsave() is not safe, since BPF prog might be called from tracepoint where preemption is disabled. So trylock only. Note, free_page and memcg are not taught about __GFP_TRYLOCK yet. The support 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/ Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> --- include/linux/gfp.h | 3 ++ include/linux/gfp_types.h | 1 + mm/internal.h | 2 ++ mm/page_alloc.c | 69 ++++++++++++++++++++++++++++++++++++--- 4 files changed, 71 insertions(+), 4 deletions(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index b0fe9f62d15b..65b8df1db26a 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -347,6 +347,9 @@ static inline struct page *alloc_page_vma_noprof(gfp_t gfp, } #define alloc_page_vma(...) alloc_hooks(alloc_page_vma_noprof(__VA_ARGS__)) +struct page *try_alloc_pages_noprof(int nid, unsigned int order); +#define try_alloc_pages(...) alloc_hooks(try_alloc_pages_noprof(__VA_ARGS__)) + extern unsigned long get_free_pages_noprof(gfp_t gfp_mask, unsigned int order); #define __get_free_pages(...) alloc_hooks(get_free_pages_noprof(__VA_ARGS__)) diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index 65db9349f905..65b148ec86eb 100644 --- a/include/linux/gfp_types.h +++ b/include/linux/gfp_types.h @@ -48,6 +48,7 @@ enum { ___GFP_THISNODE_BIT, ___GFP_ACCOUNT_BIT, ___GFP_ZEROTAGS_BIT, + ___GFP_TRYLOCK_BIT, #ifdef CONFIG_KASAN_HW_TAGS ___GFP_SKIP_ZERO_BIT, ___GFP_SKIP_KASAN_BIT, diff --git a/mm/internal.h b/mm/internal.h index cb8d8e8e3ffa..122fce7e1a9e 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1175,6 +1175,8 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, #endif #define ALLOC_HIGHATOMIC 0x200 /* Allows access to MIGRATE_HIGHATOMIC */ #define ALLOC_KSWAPD 0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */ +#define __GFP_TRYLOCK ((__force gfp_t)BIT(___GFP_TRYLOCK_BIT)) +#define ALLOC_TRYLOCK 0x1000000 /* Only use spin_trylock in allocation path */ /* Flags that allow allocations below the min watermark. */ #define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 1cb4b8c8886d..d23545057b6e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2304,7 +2304,11 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, unsigned long flags; int i; - spin_lock_irqsave(&zone->lock, flags); + if (!spin_trylock_irqsave(&zone->lock, flags)) { + if (unlikely(alloc_flags & ALLOC_TRYLOCK)) + return 0; + spin_lock_irqsave(&zone->lock, flags); + } for (i = 0; i < count; ++i) { struct page *page = __rmqueue(zone, order, migratetype, alloc_flags); @@ -2904,7 +2908,11 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, do { page = NULL; - spin_lock_irqsave(&zone->lock, flags); + if (!spin_trylock_irqsave(&zone->lock, flags)) { + if (unlikely(alloc_flags & ALLOC_TRYLOCK)) + return NULL; + spin_lock_irqsave(&zone->lock, flags); + } if (alloc_flags & ALLOC_HIGHATOMIC) page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC); if (!page) { @@ -4001,6 +4009,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order) */ BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_MIN_RESERVE); BUILD_BUG_ON(__GFP_KSWAPD_RECLAIM != (__force gfp_t) ALLOC_KSWAPD); + BUILD_BUG_ON(__GFP_TRYLOCK != (__force gfp_t) ALLOC_TRYLOCK); /* * The caller may dip into page reserves a bit more if the caller @@ -4009,7 +4018,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order) * set both ALLOC_NON_BLOCK and ALLOC_MIN_RESERVE(__GFP_HIGH). */ alloc_flags |= (__force int) - (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)); + (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM | __GFP_TRYLOCK)); if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) { /* @@ -4509,7 +4518,8 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order, might_alloc(gfp_mask); - if (should_fail_alloc_page(gfp_mask, order)) + if (!(*alloc_flags & ALLOC_TRYLOCK) && + should_fail_alloc_page(gfp_mask, order)) return false; *alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, *alloc_flags); @@ -7023,3 +7033,54 @@ static bool __free_unaccepted(struct page *page) } #endif /* CONFIG_UNACCEPTED_MEMORY */ + +struct page *try_alloc_pages_noprof(int nid, unsigned int order) +{ + gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | + __GFP_NOMEMALLOC | __GFP_TRYLOCK; + unsigned int alloc_flags = ALLOC_TRYLOCK; + struct alloc_context ac = { }; + struct page *page; + + /* + * In RT spin_trylock() may call raw_spin_lock() which is unsafe in NMI. + * If spin_trylock() is called from hard IRQ the current task may be + * waiting for one rt_spin_lock, but rt_spin_trylock() will mark the + * task as the owner of another rt_spin_lock which will confuse PI + * logic, so return immediately if called form hard IRQ or NMI. + * + * Note, irqs_disabled() case is ok. This function can be called + * from raw_spin_lock_irqsave region. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) + return NULL; + if (!pcp_allowed_order(order)) + return NULL; + +#ifdef CONFIG_UNACCEPTED_MEMORY + if (has_unaccepted_memory() && !list_empty(&zone->unaccepted_pages)) + return NULL; +#endif + + if (nid == NUMA_NO_NODE) + nid = numa_node_id(); + + prepare_alloc_pages(alloc_gfp, order, nid, NULL, &ac, + &alloc_gfp, &alloc_flags); + + /* + * Best effort allocation from percpu free list. + * If it's empty attempt to spin_trylock zone->lock. + * Do not specify __GFP_KSWAPD_RECLAIM to avoid wakeup_kswapd + * that may need to grab a lock. + * Do not specify __GFP_ACCOUNT to avoid local_lock. + * Do not warn either. + */ + page = get_page_from_freelist(alloc_gfp, order, alloc_flags, &ac); + + /* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */ + + trace_mm_page_alloc(page, order, alloc_gfp & ~__GFP_TRYLOCK, ac.migratetype); + kmsan_alloc_page(page, order, alloc_gfp); + return page; +} -- 2.43.5
