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_page() 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. There is no attempt to make free_page() to be accessible from any context (yet). BPF infrastructure will asynchronously free pages from such contexts. memcg is also not charged in try_alloc_page() path. It has to be done asynchronously to avoid sleeping on local_lock_irqsave(&memcg_stock.stock_lock, flags). 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 | 17 +++++++++++++++++ include/linux/gfp_types.h | 3 +++ include/trace/events/mmflags.h | 1 + mm/internal.h | 1 + mm/page_alloc.c | 19 ++++++++++++++++--- tools/perf/builtin-kmem.c | 1 + 6 files changed, 39 insertions(+), 3 deletions(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index a951de920e20..319d8906ef3f 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -347,6 +347,23 @@ 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_page_noprof(int nid) +{ + /* If spin_locks are not held and interrupts are enabled, use normal path. */ + if (preemptible()) + return alloc_pages_node_noprof(nid, GFP_NOWAIT | __GFP_ZERO, 0); + /* + * 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, 0); +} +#define try_alloc_page(nid) alloc_hooks(try_alloc_page_noprof(nid)) + 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/internal.h b/mm/internal.h index 64c2eb0b160e..c1b08e95a63b 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1173,6 +1173,7 @@ 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 216fbbfbedcf..71fed4f5bd0c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2304,7 +2304,12 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, unsigned long flags; int i; - spin_lock_irqsave(&zone->lock, flags); + if (unlikely(alloc_flags & ALLOC_TRYLOCK)) { + if (!spin_trylock_irqsave(&zone->lock, flags)) + return 0; + } else { + spin_lock_irqsave(&zone->lock, flags); + } for (i = 0; i < count; ++i) { struct page *page = __rmqueue(zone, order, migratetype, alloc_flags); @@ -2904,7 +2909,12 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, do { page = NULL; - spin_lock_irqsave(&zone->lock, flags); + if (unlikely(alloc_flags & ALLOC_TRYLOCK)) { + if (!spin_trylock_irqsave(&zone->lock, flags)) + return 0; + } else { + spin_lock_irqsave(&zone->lock, flags); + } if (alloc_flags & ALLOC_HIGHATOMIC) page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC); if (!page) { @@ -4001,6 +4011,7 @@ 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 +4020,7 @@ 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 +4520,8 @@ 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 a756147e2eec..d245ff60d2a6 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
