From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxx
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Acked-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/idr.c | 2 --
lib/radix-tree.c | 2 +-
2 files changed, 1 insertion(+), 3 deletions(-)
diff -puN lib/idr.c~ida-do-zeroing-in-ida_pre_get lib/idr.c
--- a/lib/idr.c~ida-do-zeroing-in-ida_pre_get
+++ a/lib/idr.c
@@ -431,7 +431,6 @@ int ida_get_new_above(struct ida *ida, i
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, i
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);
}
diff -puN lib/radix-tree.c~ida-do-zeroing-in-ida_pre_get lib/radix-tree.c
--- a/lib/radix-tree.c~ida-do-zeroing-in-ida_pre_get
+++ a/lib/radix-tree.c
@@ -2125,7 +2125,7 @@ int ida_pre_get(struct ida *ida, gfp_t g
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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