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 __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 | 25 +++++++++++++++++++++++++ include/linux/gfp_types.h | 3 +++ include/trace/events/mmflags.h | 1 + mm/fail_page_alloc.c | 6 ++++++ mm/internal.h | 1 + mm/page_alloc.c | 17 ++++++++++++++--- tools/perf/builtin-kmem.c | 1 + 7 files changed, 51 insertions(+), 3 deletions(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index b0fe9f62d15b..f68daa9c997b 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -347,6 +347,31 @@ static inline struct page *alloc_page_vma_noprof(gfp_t gfp, } #define alloc_page_vma(...) alloc_hooks(alloc_page_vma_noprof(__VA_ARGS__)) +static inline struct page *try_alloc_pages_noprof(int nid, unsigned int order) +{ + /* + * If spin_locks are not held and interrupts are enabled, use normal + * path. BPF progs run under rcu_read_lock(), so in PREEMPT_RT + * rcu_preempt_depth() will be >= 1 and will use trylock path. + */ + if (preemptible() && !rcu_preempt_depth()) + return alloc_pages_node_noprof(nid, + GFP_NOWAIT | __GFP_ZERO, + order); + /* + * 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. + */ + return alloc_pages_node_noprof(nid, + __GFP_TRYLOCK | __GFP_NOWARN | __GFP_ZERO, + 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..72b385a7888d 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, @@ -86,6 +87,7 @@ enum { #define ___GFP_THISNODE BIT(___GFP_THISNODE_BIT) #define ___GFP_ACCOUNT BIT(___GFP_ACCOUNT_BIT) #define ___GFP_ZEROTAGS BIT(___GFP_ZEROTAGS_BIT) +#define ___GFP_TRYLOCK BIT(___GFP_TRYLOCK_BIT) #ifdef CONFIG_KASAN_HW_TAGS #define ___GFP_SKIP_ZERO BIT(___GFP_SKIP_ZERO_BIT) #define ___GFP_SKIP_KASAN BIT(___GFP_SKIP_KASAN_BIT) @@ -293,6 +295,7 @@ enum { #define __GFP_COMP ((__force gfp_t)___GFP_COMP) #define __GFP_ZERO ((__force gfp_t)___GFP_ZERO) #define __GFP_ZEROTAGS ((__force gfp_t)___GFP_ZEROTAGS) +#define __GFP_TRYLOCK ((__force gfp_t)___GFP_TRYLOCK) #define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO) #define __GFP_SKIP_KASAN ((__force gfp_t)___GFP_SKIP_KASAN) diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index bb8a59c6caa2..592c93ee5f35 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -50,6 +50,7 @@ gfpflag_string(__GFP_RECLAIM), \ gfpflag_string(__GFP_DIRECT_RECLAIM), \ gfpflag_string(__GFP_KSWAPD_RECLAIM), \ + gfpflag_string(__GFP_TRYLOCK), \ gfpflag_string(__GFP_ZEROTAGS) #ifdef CONFIG_KASAN_HW_TAGS diff --git a/mm/fail_page_alloc.c b/mm/fail_page_alloc.c index 7647096170e9..b3b297d67909 100644 --- a/mm/fail_page_alloc.c +++ b/mm/fail_page_alloc.c @@ -31,6 +31,12 @@ bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order) return false; if (gfp_mask & __GFP_NOFAIL) return false; + if (gfp_mask & __GFP_TRYLOCK) + /* + * Internals of should_fail_ex() are not compatible + * with trylock concept. + */ + return false; if (fail_page_alloc.ignore_gfp_highmem && (gfp_mask & __GFP_HIGHMEM)) return false; if (fail_page_alloc.ignore_gfp_reclaim && diff --git a/mm/internal.h b/mm/internal.h index cb8d8e8e3ffa..c082b8fa1d71 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1175,6 +1175,7 @@ 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 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..d511e68903c6 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)) { /* @@ -4509,6 +4518,8 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order, might_alloc(gfp_mask); + *alloc_flags |= (__force int) (gfp_mask & __GFP_TRYLOCK); + if (should_fail_alloc_page(gfp_mask, order)) return false; diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c index 4d8d94146f8d..1f7f4269fa10 100644 --- a/tools/perf/builtin-kmem.c +++ b/tools/perf/builtin-kmem.c @@ -682,6 +682,7 @@ static const struct { { "__GFP_RECLAIM", "R" }, { "__GFP_DIRECT_RECLAIM", "DR" }, { "__GFP_KSWAPD_RECLAIM", "KR" }, + { "__GFP_TRYLOCK", "TL" }, }; static size_t max_gfp_len; -- 2.43.5
