On Fri, Jun 03, 2011 at 08:07:30PM +0200, Andrea Arcangeli wrote:
> On Fri, Jun 03, 2011 at 07:37:07PM +0200, Andrea Arcangeli wrote:
> > On Fri, Jun 03, 2011 at 08:01:44AM +0900, Minchan Kim wrote:
> > > Do you want this? (it's almost pseudo-code)
> >
> > Yes that's good idea so we at least take into account if we isolated
> > something big, and it's pointless to insist wasting CPU on the tail
> > pages and even trace a fail because of tail pages after it.
> >
> > I introduced a __page_count to increase readability. It's still
> > hackish to work on subpages in vmscan.c but at least I added a comment
> > and until we serialize destroy_compound_page vs compound_head, I guess
> > there's no better way. I didn't attempt to add out of order
> > serialization similar to what exists for split_huge_page vs
> > compound_trans_head yet, as the page can be allocated or go away from
> > under us, in split_huge_page vs compound_trans_head it's simpler
> > because both callers are required to hold a pin on the page so the
> > page can't go be reallocated and destroyed under it.
>
> Sent too fast... had to shuffle a few things around... trying again.
>
> ===
> Subject: mm: no page_count without a page pin
>
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>
> It's unsafe to run page_count during the physical pfn scan because
> compound_head could trip on a dangling pointer when reading page->first_page if
> the compound page is being freed by another CPU. Also properly take into
> account if we isolated a compound page during the scan and break the loop if
> we've isolated enoguh. Introduce __page_count to cleanup some atomic_read from
> &page->_count in common code to cleanup.
>
Patch looks good to me.
I have a question. Please see bottom line.
In addition, I think this patch have to be divided by 4 patches.
1. fix accounting nu_lumpy_taken, nr_lumpy_dirty on hpage
2. early breaking of isolate_lru_pages if we had enough isolated pages
3. introduce __page_count and cleanup
4. fix page_count usage of subpage in vmscan.c
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> ---
> arch/powerpc/mm/gup.c | 2 -
> arch/powerpc/platforms/512x/mpc512x_shared.c | 2 -
> arch/x86/mm/gup.c | 2 -
> fs/nilfs2/page.c | 2 -
> include/linux/mm.h | 13 ++++++----
> mm/huge_memory.c | 4 +--
> mm/internal.h | 2 -
> mm/page_alloc.c | 6 ++--
> mm/swap.c | 4 +--
> mm/vmscan.c | 35 ++++++++++++++++++++-------
> 10 files changed, 47 insertions(+), 25 deletions(-)
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1047,7 +1047,7 @@ static unsigned long isolate_lru_pages(u
> for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
> struct page *page;
> unsigned long pfn;
> - unsigned long end_pfn;
> + unsigned long start_pfn, end_pfn;
> unsigned long page_pfn;
> int zone_id;
>
> @@ -1087,9 +1087,9 @@ static unsigned long isolate_lru_pages(u
> */
> zone_id = page_zone_id(page);
> page_pfn = page_to_pfn(page);
> - pfn = page_pfn & ~((1 << order) - 1);
> - end_pfn = pfn + (1 << order);
> - for (; pfn < end_pfn; pfn++) {
> + start_pfn = page_pfn & ~((1 << order) - 1);
> + end_pfn = start_pfn + (1 << order);
> + for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> struct page *cursor_page;
>
> /* The target page is in the block, ignore it. */
> @@ -1116,16 +1116,33 @@ static unsigned long isolate_lru_pages(u
> break;
>
> if (__isolate_lru_page(cursor_page, mode, file) == 0) {
> + unsigned int isolated_pages;
> list_move(&cursor_page->lru, dst);
> mem_cgroup_del_lru(cursor_page);
> - nr_taken += hpage_nr_pages(page);
> - nr_lumpy_taken++;
> + isolated_pages = hpage_nr_pages(page);
> + nr_taken += isolated_pages;
> + nr_lumpy_taken += isolated_pages;
> if (PageDirty(cursor_page))
> - nr_lumpy_dirty++;
> + nr_lumpy_dirty += isolated_pages;
> scan++;
> + pfn += isolated_pages-1;
> + VM_BUG_ON(!isolated_pages);
> + VM_BUG_ON(isolated_pages > MAX_ORDER_NR_PAGES);
What's point of this VM_BUG_ONs?
Could you explain what you expect with this VM_BUG_ONs?
--
Kind regards
Minchan Kim
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