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7624e69465
So we start with:
$ pahole -C map ~/bin/perf
struct map {
union {
struct rb_node rb_node __attribute__((__aligned__(8))); /* 0 24 */
struct list_head node; /* 0 16 */
} __attribute__((__aligned__(8))); /* 0 24 */
u64 start; /* 24 8 */
u64 end; /* 32 8 */
_Bool erange_warned:1; /* 40: 0 1 */
_Bool priv:1; /* 40: 1 1 */
/* XXX 6 bits hole, try to pack */
/* XXX 3 bytes hole, try to pack */
u32 prot; /* 44 4 */
u32 flags; /* 48 4 */
/* XXX 4 bytes hole, try to pack */
u64 pgoff; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
u64 reloc; /* 64 8 */
u32 maj; /* 72 4 */
u32 min; /* 76 4 */
u64 ino; /* 80 8 */
u64 ino_generation; /* 88 8 */
u64 (*map_ip)(struct map *, u64); /* 96 8 */
u64 (*unmap_ip)(struct map *, u64); /* 104 8 */
struct dso * dso; /* 112 8 */
refcount_t refcnt; /* 120 4 */
/* size: 128, cachelines: 2, members: 17 */
/* sum members: 116, holes: 2, sum holes: 7 */
/* sum bitfield members: 2 bits, bit holes: 1, sum bit holes: 6 bits */
/* padding: 4 */
/* forced alignments: 1 */
} __attribute__((__aligned__(8)));
$
and 'flags' is seldom used when printing details about the map or with
the "cacheline" sort order, we can move them it to the second cacheline,
that will allow combining it with 'refcnt', that is only four bytes:
$ pahole -C map ~/bin/perf
struct map {
union {
struct rb_node rb_node __attribute__((__aligned__(8))); /* 0 24 */
struct list_head node; /* 0 16 */
} __attribute__((__aligned__(8))); /* 0 24 */
u64 start; /* 24 8 */
u64 end; /* 32 8 */
_Bool erange_warned:1; /* 40: 0 1 */
_Bool priv:1; /* 40: 1 1 */
/* XXX 6 bits hole, try to pack */
/* XXX 3 bytes hole, try to pack */
u32 prot; /* 44 4 */
u64 pgoff; /* 48 8 */
u64 reloc; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
u32 maj; /* 64 4 */
u32 min; /* 68 4 */
u64 ino; /* 72 8 */
u64 ino_generation; /* 80 8 */
u64 (*map_ip)(struct map *, u64); /* 88 8 */
u64 (*unmap_ip)(struct map *, u64); /* 96 8 */
struct dso * dso; /* 104 8 */
refcount_t refcnt; /* 112 4 */
u32 flags; /* 116 4 */
/* size: 120, cachelines: 2, members: 17 */
/* sum members: 116, holes: 1, sum holes: 3 */
/* sum bitfield members: 2 bits, bit holes: 1, sum bit holes: 6 bits */
/* forced alignments: 1 */
/* last cacheline: 56 bytes */
} __attribute__((__aligned__(8)));
$
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-2cdw3zlw1mkamaf7nqtdlxfi@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.