Commit b1a8a7a7 authored Feb 21, 2018 by Rasmus Villemoes Committed by Linus Torvalds Feb 21, 2018

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: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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))

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