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.
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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