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

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