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> > > #ifdef CONFIG_SECURITY > > > void *security; > > > #endif > > > > > > > u32 value_size; > u32 max_entries; > u32 map_flags; > + u64 > > > map_extra; /* any per-map-type extra fields */ There is a 4 byte > > > hole before the new 'u64 map_extra'. Try to move > > > it before map_flags > > Manually resuscitating your previous comment back into this email ^. > > After rebasing to the latest master, I'm not seeing a significant difference > anymore with map_extra before/after max_flags. This is what I see when > running "pahole vmlinux.o": > > With map_extra AFTER map_flags: > > struct bpf_map { >         const struct bpf_map_ops  * ops __attribute__((__aligned__(64))); > /*     0     8 */ >         struct bpf_map *           inner_map_meta;       /* 8     8 */ >         void *                     security;             /* 16     8 */ >         enum bpf_map_type          map_type;             /* 24     4 */ >         u32                        key_size;             /* 28     4 */ >         u32                        value_size;           /* 32     4 */ >         u32                        max_entries;          /* 36     4 */ >         u32                        map_flags;            /* 40     4 */ > >         /* XXX 4 bytes hole, try to pack */ > >         u64                        map_extra;            /* 48     8 */ >         int                        spin_lock_off;        /* 56     4 */ >         int                        timer_off;            /* 60     4 */ >         /* --- cacheline 1 boundary (64 bytes) --- */ >         u32                        id;                   /* 64     4 */ >         int                        numa_node;            /* 68     4 */ >         u32                        btf_key_type_id;      /* 72     4 */ >         u32                        btf_value_type_id;    /* 76     4 */ >         struct btf *               btf;                  /* 80     8 */ >         struct mem_cgroup *        memcg;                /* 88     8 */ >         char                       name[16];             /* 96    16 */ >         u32                        btf_vmlinux_value_type_id; /* 112     4 > */ >         bool                       bypass_spec_v1;       /* 116     1 */ >         bool                       frozen;               /* 117     1 */ > >         /* XXX 10 bytes hole, try to pack */ > >         /* --- cacheline 2 boundary (128 bytes) --- */ >         atomic64_t                 refcnt __attribute__((__aligned__(64))); > /*   128     8 */ >         atomic64_t                 usercnt;              /* 136     8 */ >         struct work_struct         work;                 /* 144    72 */ >         /* --- cacheline 3 boundary (192 bytes) was 24 bytes ago --- */ >         struct mutex               freeze_mutex;         /* 216   144 */ >         /* --- cacheline 5 boundary (320 bytes) was 40 bytes ago --- */ >         u64                        writecnt;             /* 360     8 */ > >         /* size: 384, cachelines: 6, members: 26 */ >         /* sum members: 354, holes: 2, sum holes: 14 */ >         /* padding: 16 */ >         /* forced alignments: 2, forced holes: 1, sum forced holes: 10 */ > } __attribute__((__aligned__(64))); > > > With map_extra BEFORE map_flags: > > struct bpf_map { >         const struct bpf_map_ops  * ops __attribute__((__aligned__(64))); > /*     0     8 */ >         struct bpf_map *           inner_map_meta;       /* 8     8 */ >         void *                     security;             /* 16     8 */ >         enum bpf_map_type          map_type;             /* 24     4 */ >         u32                        key_size;             /* 28     4 */ >         u32                        value_size;           /* 32     4 */ >         u32                        max_entries;          /* 36     4 */ >         u64                        map_extra;            /* 40     8 */ >         u32                        map_flags;            /* 48     4 */ >         int                        spin_lock_off;        /* 52     4 */ >         int                        timer_off;            /* 56     4 */ >         u32                        id;                   /* 60     4 */ >         /* --- cacheline 1 boundary (64 bytes) --- */ >         int                        numa_node;            /* 64     4 */ >         u32                        btf_key_type_id;      /* 68     4 */ >         u32                        btf_value_type_id;    /* 72     4 */ > >         /* XXX 4 bytes hole, try to pack */ > >         struct btf *               btf;                  /* 80     8 */ >         struct mem_cgroup *        memcg;                /* 88     8 */ >         char                       name[16];             /* 96    16 */ >         u32                        btf_vmlinux_value_type_id; /* 112     4 > */ >         bool                       bypass_spec_v1;       /* 116     1 */ >         bool                       frozen;               /* 117     1 */ > >         /* XXX 10 bytes hole, try to pack */ > >         /* --- cacheline 2 boundary (128 bytes) --- */ >         atomic64_t                 refcnt __attribute__((__aligned__(64))); > /*   128     8 */ >         atomic64_t                 usercnt;              /* 136     8 */ >         struct work_struct         work;                 /* 144    72 */ >         /* --- cacheline 3 boundary (192 bytes) was 24 bytes ago --- */ >         struct mutex               freeze_mutex;         /* 216   144 */ >         /* --- cacheline 5 boundary (320 bytes) was 40 bytes ago --- */ >         u64                        writecnt;             /* 360     8 */ > >         /* size: 384, cachelines: 6, members: 26 */ >         /* sum members: 354, holes: 2, sum holes: 14 */ >         /* padding: 16 */ >         /* forced alignments: 2, forced holes: 1, sum forced holes: 10 */ > } __attribute__((__aligned__(64))); > > > The main difference is that the "id" field is part of the 2nd cacheline when > "map_extra" is after "map_flags", and is part of the 1st cacheline when > "map_extra" is before "map_flags". > > Do you think it's still worth it to move "map_extra" to before "map_flags"? It looks like there is an existing 4 byte hole. I would take this chance to plunge it by using an existing 4 byte field. Something like this: diff --git i/include/linux/bpf.h w/include/linux/bpf.h index 50105e0b8fcc..0e07c659acd4 100644 --- i/include/linux/bpf.h +++ w/include/linux/bpf.h @@ -169,22 +169,22 @@ struct bpf_map { u32 value_size; u32 max_entries; u32 map_flags; - u64 map_extra; /* any per-map-type extra fields */ int spin_lock_off; /* >=0 valid offset, <0 error */ int timer_off; /* >=0 valid offset, <0 error */ u32 id; int numa_node; u32 btf_key_type_id; u32 btf_value_type_id; + u32 btf_vmlinux_value_type_id; + u64 map_extra; /* any per-map-type extra fields */ struct btf *btf; #ifdef CONFIG_MEMCG_KMEM struct mem_cgroup *memcg; #endif char name[BPF_OBJ_NAME_LEN]; - u32 btf_vmlinux_value_type_id; bool bypass_spec_v1; bool frozen; /* write-once; write-protected by freeze_mutex */ - /* 22 bytes hole */ + /* 14 bytes hole */ /* The 3rd and 4th cacheline with misc members to avoid false sharing * particularly with refcounting.