Re: [PATCH] writeback: initialize m_dirty to avoid compile warning

From: Shi, Yang
Date: Wed Nov 18 2015 - 13:27:38 EST

On 11/18/2015 10:11 AM, Tejun Heo wrote:

On Tue, Nov 17, 2015 at 03:38:55PM -0800, Andrew Morton wrote:
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1542,7 +1542,7 @@ static void balance_dirty_pages(struct address_space *mapping,
for (;;) {
unsigned long now = jiffies;
unsigned long dirty, thresh, bg_thresh;
- unsigned long m_dirty, m_thresh, m_bg_thresh;
+ unsigned long m_dirty = 0, m_thresh = 0, m_bg_thresh = 0;

* Unstable writes are a feature of certain networked

Adding runtime overhead to suppress a compile-time warning is Just

With gcc-4.4.4 the above patch actually reduces page-writeback.o's
.text by 36 bytes, lol. With gcc-4.8.4 the patch saves 19 bytes. No
idea what's going on there...

And initializing locals in the above fashion can hide real bugs -

This was the main reason the code was structured the way it is. If
cgroup writeback is not enabled, any derefs of mdtc variables should
trigger warnings. Ugh... I don't know. Compiler really should be
able to tell this much.

Thanks for the explanation. It sounds like a compiler problem.

If you think it is still good to cease the compile warning, maybe we could just assign it to an insane value as what Andrew suggested, maybe 0xdeadbeef.



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