From b1a8a7a70043400d1e685899548c92b92f640d71 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Wed, 21 Feb 2018 14:45:43 -0800 Subject: [PATCH] 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 Acked-by: Matthew Wilcox Cc: Eric Biggers Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/idr.c | 2 -- lib/radix-tree.c | 2 +- 2 files changed, 1 insertion(+), 3 deletions(-) diff --git a/lib/idr.c b/lib/idr.c index c98d77f..99ec5bc 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -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); } diff --git a/lib/radix-tree.c b/lib/radix-tree.c index 0a7ae32..8e00138 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -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)) -- 2.7.4