On Tue, Jul 14, 2015 at 02:07:08PM -0700, Andrew Morton wrote:
> On Mon, 15 Jun 2015 22:06:54 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> > We want to know per-process workingset size for smart memory management
> > on userland and we use swap(ex, zram) heavily to maximize memory efficiency
> > so workingset includes swap as well as RSS.
> >
> > On such system, if there are lots of shared anonymous pages, it's
> > really hard to figure out exactly how many each process consumes
> > memory(ie, rss + wap) if the system has lots of shared anonymous
> > memory(e.g, android).
> >
> > This patch introduces SwapPss field on /proc/<pid>/smaps so we can get
> > more exact workingset size per process.
> >
> > ...
> >
> > +int swp_swapcount(swp_entry_t entry)
> > +{
> > + int count, tmp_count, n;
> > + struct swap_info_struct *p;
> > + struct page *page;
> > + pgoff_t offset;
> > + unsigned char *map;
> > +
> > + p = swap_info_get(entry);
> > + if (!p)
> > + return 0;
> > +
> > + count = swap_count(p->swap_map[swp_offset(entry)]);
> > + if (!(count & COUNT_CONTINUED))
> > + goto out;
> > +
> > + count &= ~COUNT_CONTINUED;
> > + n = SWAP_MAP_MAX + 1;
> > +
> > + offset = swp_offset(entry);
> > + page = vmalloc_to_page(p->swap_map + offset);
> > + offset &= ~PAGE_MASK;
> > + VM_BUG_ON(page_private(page) != SWP_CONTINUED);
> > +
> > + do {
> > + page = list_entry(page->lru.next, struct page, lru);
> > + map = kmap_atomic(page) + offset;
> > + tmp_count = *map;
> > + kunmap_atomic(map);
>
> A little thing: I've never liked the way that kunmap_atomic() accepts
> any address within the page. It's weird, and it makes the reviewer
> have to scramble around to make sure the offset can never be >=
> PAGE_SIZE.
Very ture. I was bitten by that.
Thanks for the clean up.
>
> We can easily avoid doing it here:
>
> --- a/mm/swapfile.c~mm-show-proportional-swap-share-of-the-mapping-fix
> +++ a/mm/swapfile.c
> @@ -904,8 +904,8 @@ int swp_swapcount(swp_entry_t entry)
>
> do {
> page = list_entry(page->lru.next, struct page, lru);
> - map = kmap_atomic(page) + offset;
> - tmp_count = *map;
> + map = kmap_atomic(page);
> + tmp_count = map[offset];
> kunmap_atomic(map);
>
> count += (tmp_count & ~COUNT_CONTINUED) * n;
>
> > + count += (tmp_count & ~COUNT_CONTINUED) * n;
> > + n *= (SWAP_CONT_MAX + 1);
> > + } while (tmp_count & COUNT_CONTINUED);
> > +out:
> > + spin_unlock(&p->lock);
> > + return count;
> > +}
> >
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