Re: [PATCH 03/16] page-flags: introduce page flags policies wrt compound pages

[Konstantin Khlebnikov]

On 28.09.2015 14:03, Kirill A. Shutemov wrote:
> On Mon, Sep 28, 2015 at 01:02:19PM +0300, Konstantin Khlebnikov wrote:
> > On 25.09.2015 22:13, Kirill A. Shutemov wrote:
> > > On Fri, Sep 25, 2015 at 03:29:17PM +0300, Konstantin Khlebnikov wrote:
> > > > On 24.09.2015 17:50, Kirill A. Shutemov wrote:
> > > > > This patch adds a third argument to macros which create function
> > > > > definitions for page flags.  This argument defines how page-flags helpers
> > > > > behave on compound functions.
> > > > >
> > > > > For now we define four policies:
> > > > >
> > > > > - PF_ANY: the helper function operates on the page it gets, regardless
> > > > >    if it's non-compound, head or tail.
> > > > >
> > > > > - PF_HEAD: the helper function operates on the head page of the compound
> > > > >    page if it gets tail page.
> > > > >
> > > > > - PF_NO_TAIL: only head and non-compond pages are acceptable for this
> > > > >    helper function.
> > > > >
> > > > > - PF_NO_COMPOUND: only non-compound pages are acceptable for this helper
> > > > >    function.
> > > > >
> > > > > For now we use policy PF_ANY for all helpers, which matches current
> > > > > behaviour.
> > > > >
> > > > > We do not enforce the policy for TESTPAGEFLAG, because we have flags
> > > > > checked for random pages all over the kernel.  Noticeable exception to
> > > > > this is PageTransHuge() which triggers VM_BUG_ON() for tail page.
> > > > >
> > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > > > ---
> > > > >   include/linux/page-flags.h | 154 ++++++++++++++++++++++++++-------------------
> > > > >   1 file changed, 90 insertions(+), 64 deletions(-)
> > > > >
> > > > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > > > > index 713d3f2c2468..1b3babe5ff69 100644
> > > > > --- a/include/linux/page-flags.h
> > > > > +++ b/include/linux/page-flags.h
> > > > > @@ -154,49 +154,68 @@ static inline int PageCompound(struct page *page)
> > > > >   	return test_bit(PG_head, &page->flags) || PageTail(page);
> > > > >   }
> > > > >
> > > > > +/* Page flags policies wrt compound pages */
> > > > > +#define PF_ANY(page, enforce)	page
> > > > > +#define PF_HEAD(page, enforce)	compound_head(page)
> > > > > +#define PF_NO_TAIL(page, enforce) ({					\
> > > > > +		if (enforce)						\
> > > > > +			VM_BUG_ON_PAGE(PageTail(page), page);		\
> > > > > +		else							\
> > > > > +			page = compound_head(page);			\
> > > > > +		page;})
> > > > > +#define PF_NO_COMPOUND(page, enforce) ({					\
> > > > > +		if (enforce)						\
> > > > > +			VM_BUG_ON_PAGE(PageCompound(page), page);	\
> > > >
> > > > Linux next-20150925 crashes here (at least in lkvm)
> > > > if CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
> > >
> > > Hm. I don't see the crash in qemu. Could you share your config?
> >
> > see in attachment
>
> Still don't see it. Have you tried patch from my previous mail?

Just checked: patch fixes oops.


This part of 7e18adb4f80bea90d30b62158694d97c31f71d37
(mm: meminit: initialise remaining struct pages in parallel with kswapd)
is unclear:

+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+static void init_reserved_page(unsigned long pfn)
+{
+       pg_data_t *pgdat;
+       int nid, zid;
+
+       if (!early_page_uninitialised(pfn))
+               return;
+
+       nid = early_pfn_to_nid(pfn);
+       pgdat = NODE_DATA(nid);
+
+       for (zid = 0; zid < MAX_NR_ZONES; zid++) {
+               struct zone *zone = &pgdat->node_zones[zid];
+
+               if (pfn >= zone->zone_start_pfn && pfn < zone_end_pfn(zone))
+                       break;
+       }
+       __init_single_pfn(pfn, zid, nid);
+}
+#else
+static inline void init_reserved_page(unsigned long pfn)
+{
+}
+#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
+
 /*
  * Initialised pages do not have PageReserved set. This function is
  * called for each range allocated by the bootmem allocator and
  * marks the pages PageReserved. The remaining valid pages are later
  * sent to the buddy page allocator.
  */
-void reserve_bootmem_region(unsigned long start, unsigned long end)
+void __meminit reserve_bootmem_region(unsigned long start, unsigned 
long end)
 {
        unsigned long start_pfn = PFN_DOWN(start);
        unsigned long end_pfn = PFN_UP(end);

-       for (; start_pfn < end_pfn; start_pfn++)
-               if (pfn_valid(start_pfn))
-                       SetPageReserved(pfn_to_page(start_pfn));
+       for (; start_pfn < end_pfn; start_pfn++) {
+               if (pfn_valid(start_pfn)) {
+                       struct page *page = pfn_to_page(start_pfn);
+
+                       init_reserved_page(start_pfn);
+                       SetPageReserved(page);
+               }
+       }
 }

We leave struct page uninitialized but call SetPageReserved for it.

--
Konstantin
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