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ida: do zeroing in ida_pre_get()

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As far as I can tell, the only place the per-cpu ida_bitmap is populated
is in ida_pre_get.  The pre-allocated element is stolen in two places in
ida_get_new_above, in both cases immediately followed by a memset(0).

Since ida_get_new_above is called with locks held, do the zeroing in
ida_pre_get, or rather let kmalloc() do it.  Also, apparently gcc
generates ~44 bytes of code to do a memset(, 0, 128):

  $ scripts/bloat-o-meter vmlinux.{0,1}
  add/remove: 0/0 grow/shrink: 2/1 up/down: 5/-88 (-83)
  Function                                     old     new   delta
  ida_pre_get                                  115     119      +4
  vermagic                                      27      28      +1
  ida_get_new_above                            715     627     -88

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Rasmus Villemoes <[email protected]>
Acked-by: Matthew Wilcox <[email protected]>
Cc: Eric Biggers <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Rasmus Villemoes 2018-02-21 14:45:43 -08:00 • committed by Linus Torvalds
commit b1a8a7a700
2 changed files with 1 additions and 3 deletions
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2
lib/idr.c
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@ -431,7 +431,6 @@ int ida_get_new_above(struct ida *ida, int start, int *id)
bitmap = this_cpu_xchg(ida_bitmap, NULL);
if (!bitmap)
return -EAGAIN;
memset(bitmap, 0, sizeof(*bitmap));
bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
rcu_assign_pointer(*slot, bitmap);
}
@ -464,7 +463,6 @@ int ida_get_new_above(struct ida *ida, int start, int *id)
bitmap = this_cpu_xchg(ida_bitmap, NULL);
if (!bitmap)
return -EAGAIN;
memset(bitmap, 0, sizeof(*bitmap));
__set_bit(bit, bitmap->bitmap);
radix_tree_iter_replace(root, &iter, slot, bitmap);
}