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Commit b1a8a7a7 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Linus Torvalds
Browse files

ida: do zeroing in ida_pre_get() 

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/20180108225634.15340-1-linux@rasmusvillemoes.dk


Signed-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: default avatarMatthew Wilcox <mawilcox@microsoft.com>
Cc: Eric Biggers <ebiggers@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7ba71669

lib/idr.c

+0 −2
Original line number Diff line number Diff line
@@ -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);

		}

lib/radix-tree.c

+1 −1
Original line number Diff line number Diff line
@@ -2125,7 +2125,7 @@ int ida_pre_get(struct ida *ida, gfp_t gfp) 
		preempt_enable();



	if (!this_cpu_read(ida_bitmap)) {

		struct ida_bitmap *bitmap = kmalloc(sizeof(*bitmap), gfp);

		struct ida_bitmap *bitmap = kzalloc(sizeof(*bitmap), gfp);

		if (!bitmap)

			return 0;

		if (this_cpu_cmpxchg(ida_bitmap, NULL, bitmap))