Re: [Lse-tech] Re: [PATCH] [0/6] HUGETLB memory commitment

[Suparna Bhattacharya <suparna@in.ibm.com>]

On Thu, Mar 25, 2004 at 04:22:32PM -0800, Andrew Morton wrote:
> Keith Owens <kaos@sgi.com> wrote:
> >
> > FWIW, lkcd (crash dump) treats hugetlb pages as normal kernel pages and
> > dumps them, which is pointless and wastes a lot of time.  To avoid
> > dumping these pages in lkcd, I had to add a PG_hugetlb flag.  lkcd runs

This should already be fixed in recent versions of lkcd. It uses a
little bit of trickery to avoid an extra page flag -- hugetlb pages are 
detected as "in use" as well as reserved, unlike other reserved pages 
which helps identify them.

/* to track all used (compound + zero order) pages */
#define PageInuse(p)   (PageCompound(p) || page_count(p))

.
.

static inline int kernel_page(struct page *p)
{
        /* Need to exclude hugetlb pages. Clue: reserved but inuse */
        return (PageReserved(p) && !PageInuse(p)) || (!PageLRU(p) && PageInuse(p));
}

Regards
Suparna

> > at the page level, not mm or vma, so VM_hugetlb was not available.  In
> > set_hugetlb_mem_size()
> > 
> > 	for (j = 0; j < (HPAGE_SIZE / PAGE_SIZE); j++) {
> > 		SetPageReserved(map);
> > 		SetPageHugetlb(map);
> > 		map++;
> > 	}
> > 
> > In dump_base.c, I changed kernel_page(), referenced_page() and
> > unreferenced_page() to test for PageHugetlb() before PageReserved().
> 
> That makes sense.
> 
> > Since you are looking at identifying hugetlb pages, could any other
> > code benefit from a PG_hugetlb flag?
> 
> In the overcommit code we don't actually have the page yet.  We're asking
> "do we have enough memory available to honour this mmap() invokation when
> it later faults in real pages".
> 
> 
> 
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-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India