Re: [PATCH] generic: test swapping process pages in and out of a swapfile

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Aug 19, 2021 at 07:56:43PM +0100, Matthew Wilcox wrote:
> On Thu, Aug 19, 2021 at 11:26:46AM -0700, Darrick J. Wong wrote:
> > +	printf("Dirtying memory.\n");
> > +	fflush(stdout);
> > +
> > +	/* Dirty the memory to force this program to be swapped out. */
> > +	for (p = pstart; p < pend; p += pagesize)
> > +		*p = 'X';
> 
> What I liked about dhowells' program was that it checked whether the
> pages brought back in from swap were the same ones that had been written
> to swap.  As a block filesystem person, you only know the misery of having
> swap go behind your back to the block device.  As a network filesystem
> person, David is acutely aware of the misery of having to remember to
> use page_file_index() instead of page->index in order to avoid reading
> a page from the wrong offset in the swap partition.
> 
> Yes, our swap code is nasty in many different ways, why do you ask?

Wheeee, I'll go change it to store per-page data in each page and check
it on the way back.

--D