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SubjectRe: [PATCH 2/4] alloc_contig_pages() find appropriate physical memory range
On Mon, 22 Nov 2010 20:20:14 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

> On Fri, Nov 19, 2010 at 5:14 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> >
> > Unlike memory hotplug, at an allocation of contigous memory range, address
> > may not be a problem. IOW, if a requester of memory wants to allocate 100M of
> > of contigous memory, placement of allocated memory may not be a problem.
> > So, "finding a range of memory which seems to be MOVABLE" is required.
> >
> > This patch adds a functon to isolate a length of memory within [start, end).
> > This function returns a pfn which is 1st page of isolated contigous chunk
> > of given length within [start, end).
> >
> > If no_search=true is passed as argument, start address is always same to
> > the specified "base" addresss.
> >
> > After isolation, free memory within this area will never be allocated.
> > But some pages will remain as "Used/LRU" pages. They should be dropped by
> > page reclaim or migration.
> >
> > Changelog: 2010-11-17
> >  - fixed some conding style (if-then-else)
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > ---
> >  mm/page_isolation.c |  146 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 146 insertions(+)
> >
> > Index: mmotm-1117/mm/page_isolation.c
> > ===================================================================
> > --- mmotm-1117.orig/mm/page_isolation.c
> > +++ mmotm-1117/mm/page_isolation.c
> > @@ -7,6 +7,7 @@
> >  #include <linux/pageblock-flags.h>
> >  #include <linux/memcontrol.h>
> >  #include <linux/migrate.h>
> > +#include <linux/memory_hotplug.h>
> >  #include <linux/mm_inline.h>
> >  #include "internal.h"
> >
> > @@ -250,3 +251,148 @@ int do_migrate_range(unsigned long start
> >  out:
> >        return ret;
> >  }
> > +
> > +/*
> > + * Functions for getting contiguous MOVABLE pages in a zone.
> > + */
> > +struct page_range {
> > +       unsigned long base; /* Base address of searching contigouous block */
> > +       unsigned long end;
> > +       unsigned long pages;/* Length of contiguous block */
>
> Nitpick.
> You used nr_pages in other place.
> I hope you use the name consistent.
>
Sure, I'll fix it.

> > +       int align_order;
> > +       unsigned long align_mask;
>
> Does we really need this field 'align_mask'?

No.

> We can get always from align_order.
>

Always writes ((1 << align_order) -1) ? Hmm.


> > +};
> > +
> > +int __get_contig_block(unsigned long pfn, unsigned long nr_pages, void *arg)
> > +{
> > +       struct page_range *blockinfo = arg;
> > +       unsigned long end;
> > +
> > +       end = pfn + nr_pages;
> > +       pfn = ALIGN(pfn, 1 << blockinfo->align_order);
> > +       end = end & ~(MAX_ORDER_NR_PAGES - 1);
> > +
> > +       if (end < pfn)
> > +               return 0;
> > +       if (end - pfn >= blockinfo->pages) {
> > +               blockinfo->base = pfn;
> > +               blockinfo->end = end;
> > +               return 1;
> > +       }
> > +       return 0;
> > +}
> > +
> > +static void __trim_zone(struct zone *zone, struct page_range *range)
> > +{
> > +       unsigned long pfn;
> > +       /*
> > +        * skip pages which dones'nt under the zone.
>
> typo dones'nt -> doesn't :)
>
will fix.

> > +        * There are some archs which zones are not in linear layout.
> > +        */
> > +       if (page_zone(pfn_to_page(range->base)) != zone) {
> > +               for (pfn = range->base;
> > +                       pfn < range->end;
> > +                       pfn += MAX_ORDER_NR_PAGES) {
> > +                       if (page_zone(pfn_to_page(pfn)) == zone)
> > +                               break;
> > +               }
> > +               range->base = min(pfn, range->end);
> > +       }
> > +       /* Here, range-> base is in the zone if range->base != range->end */
> > +       for (pfn = range->base;
> > +            pfn < range->end;
> > +            pfn += MAX_ORDER_NR_PAGES) {
> > +               if (zone != page_zone(pfn_to_page(pfn))) {
> > +                       pfn = pfn - MAX_ORDER_NR_PAGES;
> > +                       break;
> > +               }
> > +       }
> > +       range->end = min(pfn, range->end);
> > +       return;
>
> Remove return
>
Ah, ok.

> > +}
> > +
> > +/*
> > + * This function is for finding a contiguous memory block which has length
> > + * of pages and MOVABLE. If it finds, make the range of pages as ISOLATED
> > + * and return the first page's pfn.
> > + * This checks all pages in the returned range is free of Pg_LRU. To reduce
> > + * the risk of false-positive testing, lru_add_drain_all() should be called
> > + * before this function to reduce pages on pagevec for zones.
> > + */
> > +
> > +static unsigned long find_contig_block(unsigned long base,
> > +               unsigned long end, unsigned long pages,
> > +               int align_order, struct zone *zone)
> > +{
> > +       unsigned long pfn, pos;
> > +       struct page_range blockinfo;
> > +       int ret;
> > +
> > +       VM_BUG_ON(pages & (MAX_ORDER_NR_PAGES - 1));
> > +       VM_BUG_ON(base & ((1 << align_order) - 1));
> > +retry:
> > +       blockinfo.base = base;
> > +       blockinfo.end = end;
> > +       blockinfo.pages = pages;
> > +       blockinfo.align_order = align_order;
> > +       blockinfo.align_mask = (1 << align_order) - 1;
>
> We don't need this.
>
mask ?

> > +       /*
> > +        * At first, check physical page layout and skip memory holes.
> > +        */
> > +       ret = walk_system_ram_range(base, end - base, &blockinfo,
> > +               __get_contig_block);
> > +       if (!ret)
> > +               return 0;
> > +       /* check contiguous pages in a zone */
> > +       __trim_zone(zone, &blockinfo);
> > +
> > +       /*
> > +        * Ok, we found contiguous memory chunk of size. Isolate it.
> > +        * We just search MAX_ORDER aligned range.
> > +        */
> > +       for (pfn = blockinfo.base; pfn + pages <= blockinfo.end;
> > +            pfn += (1 << align_order)) {
> > +               struct zone *z = page_zone(pfn_to_page(pfn));
> > +               if (z != zone)
> > +                       continue;
>
> Could we make sure pass __trim_zone is to satisfy whole pfn in zone
> what we want.
> Repeated the zone check is rather annoying.
> I mean let's __get_contig_block or __trim_zone already does check zone
> so that we remove the zone check in here.

Ah, yes. I'll remove this.

>
> > +
> > +               spin_lock_irq(&z->lock);
> > +               pos = pfn;
> > +               /*
> > +                * Check the range only contains free pages or LRU pages.
> > +                */
> > +               while (pos < pfn + pages) {
> > +                       struct page *p;
> > +
> > +                       if (!pfn_valid_within(pos))
> > +                               break;
> > +                       p = pfn_to_page(pos);
> > +                       if (PageReserved(p))
> > +                               break;
> > +                       if (!page_count(p)) {
> > +                               if (!PageBuddy(p))
> > +                                       pos++;
> > +                               else
> > +                                       pos += (1 << page_order(p));
> > +                       } else if (PageLRU(p)) {
>
> Could we check get_pageblock_migratetype(page) == MIGRATE_MOVABLE in
> here and early bail out?
>

I'm not sure that's very good. pageblock-type can be fragmented and even
if pageblock-type is not MIGRATABLE, all pages in pageblock may be free.
Because PageLRU() is checked, all required 'quick' check is done, I think.


> > +                               pos++;
> > +                       } else
> > +                               break;
> > +               }
> > +               spin_unlock_irq(&z->lock);
> > +               if ((pos == pfn + pages)) {
> > +                       if (!start_isolate_page_range(pfn, pfn + pages))
> > +                               return pfn;
> > +               } else/* the chunk including "pos" should be skipped */
> > +                       pfn = pos & ~((1 << align_order) - 1);
> > +               cond_resched();
> > +       }
> > +
> > +       /* failed */
> > +       if (blockinfo.end + pages <= end) {
> > +               /* Move base address and find the next block of RAM. */
> > +               base = blockinfo.end;
> > +               goto retry;
> > +       }
> > +       return 0;
>
> If the base is 0, isn't it impossible return pfn 0?
> x86 in FLAT isn't impossible but I think some architecture might be possible.
> Just guessing.
>
> How about returning negative value and return first page pfn and last
> page pfn as out parameter base, end?
>

Hmm, will add a check.

Thanks,
-Kame


> > +}
> >
> >
>
>
>
> --
> Kind regards,
> Minchan Kim
> --
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