Re: [PATCH v2] mm: BUG when __kmap_atomic_idx equals KM_TYPE_NR

From: Chintan Pandya
Date: Mon Aug 04 2014 - 05:25:34 EST


On 08/01/2014 04:15 AM, Andrew Morton wrote:
On Thu, 31 Jul 2014 14:58:58 +0530 Chintan Pandya<cpandya@xxxxxxxxxxxxxx> wrote:


I think Andrew's comment earlier was referring to the changelog only and
not the patch, which looked correct.

I think Andrew asked for a BUG case details also to justify the
overhead. But we have never encountered that BUG case. Present patch is
only logical fix to the code. However, in the fast path, if such
overhead is allowed, I can move BUG_ON out of any debug configs.
Otherwise, as per Andrew's suggestion, I will convert DEBUG_HIGHMEM into
DEBUG_VM which is used more frequently.

The v1 patch added a small amount of overhead to kmap_atomic() for what
is evidently a very small benefit.

Yes, I suggest we remove CONFIG_DEBUG_HIGHMEM from the kernel entirely
and switch all CONFIG_DEBUG_HIGHMEM sites to use CONFIG_DEBUG_VM. That way
the BUG_ON which you believe is useful will be tested by more people
more often.

Ping!! Anything open for me to do here ?

--
Chintan Pandya

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