Re: [PATCH] mm: dump page when hitting a VM_BUG_ON using VM_BUG_ON_PAGE

From: Sasha Levin
Date: Fri Dec 27 2013 - 17:19:57 EST

On 12/27/2013 05:38 AM, Kirill A. Shutemov wrote:
On Thu, Dec 26, 2013 at 10:20:52PM -0500, Sasha Levin wrote:
Most of the VM_BUG_ON assertions are performed on a page. Usually, when
one of these assertions fails we'll get a BUG_ON with a call stack and
the registers.

I've recently noticed based on the requests to add a small piece of code
that dumps the page to various VM_BUG_ON sites that the page dump is quite
useful to people debugging issues in mm.

This patch adds a VM_BUG_ON_PAGE(cond, page) which beyond doing what
VM_BUG_ON() does, also dumps the page before executing the actual BUG_ON.

Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>

I like the idea. One thing I've noticed you have a lot of page flag based
asserts, like:

VM_BUG_ON_PAGE(PageLRU(page), page);
VM_BUG_ON_PAGE(!PageLocked(page), page);

What about adding per-page-flag assert macros, like:


? This way we will always dump right page on bug.

Sure, sounds good.

I'll send another patch on top of this one.

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