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SubjectRe: [patch] sg: simplify page_count manipulations
Nick Piggin <npiggin@suse.de> wrote:
>
> On Wed, Jan 18, 2006 at 07:59:37PM -0800, Andrew Morton wrote:
> > Nick Piggin <npiggin@suse.de> wrote:
> > > - /* N.B. correction _not_ applied to base page of each allocation */
> > > - for (k = 0; k < rsv_schp->k_use_sg; ++k, ++sg) {
> > > - for (m = PAGE_SIZE; m < sg->length; m += PAGE_SIZE) {
> > > - page = sg->page;
> > > - if (startFinish)
> > > - get_page(page);
> > > - else {
> > > - if (page_count(page) > 0)
> > > - __put_page(page);
> > > - }
> > > - }
> > > - }
> > > -}
> >
> > What on earth is the above trying to do? The inner loop is a rather
> > complex way of doing atomic_add(&page->count, sg->length/PAGE_SIZE). One
> > suspects there's a missing "[m]" in there.
> >
>
> It does this on the first mmap of the device, in the hope that subsequent
> nopage, unmaps would not free the constituent pages in the scatterlist.
>

But it's doing it wrongly, isn't it? Or am I completely nuts?

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