Re: [PATCH RFC v2 2/2] mm: Rework swap handling of zap_pte_range

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 16, 2021 at 12:51:13AM -0800, John Hubbard wrote:
> On 11/15/21 05:57, Matthew Wilcox wrote:
> > On Mon, Nov 15, 2021 at 09:49:51PM +0800, Peter Xu wrote:
> > > Clean the code up by merging the device private/exclusive swap entry handling
> > > with the rest, then we merge the pte clear operation too.
> > > 
> > > struct* page is defined in multiple places in the function, move it upward.
> > 
> > Is that actually a good thing?  There was a time when declaring
> 
> Yes. It is a very good thing. Having multiple cases of shadowed variables
> (in this case I'm using programming language terminology, or what I
> remember it as, anyway) provides lots of opportunities to create
> hard-to-spot bugs.

I think you're misremembering.  These are shadowed variables:

int a;

int b(void)
{
	int a;
	if (c) {
		int a;
	}
}

This is not:

int b(void)
{
	if (c) {
		int a;
	} else {
		int a;
	}
}

I really wish we could turn on -Wshadow, but we get compilation warnings
from header files right now.  Or we did last time I checked.