Messages in this thread Patch in this message | | | Date | Wed, 30 Apr 2008 14:35:42 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression: deadlock on coredump of big process) |
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On Wed, 30 Apr 2008 07:19:32 +0200 Nick Piggin <npiggin@suse.de> wrote:
> > Something like this should do: > if (!pte_present(pte)) { > if (pte_none(pte)) { > pte_unmap_unlock > goto null_or_zeropage; > } > goto unlock; > } > Sorry for broken work and thank you for advice. updated.
Regards, -Kame == follow_page() returns ZERO_PAGE if a page table is not available. but returns NULL if a page table exists. If NULL, handle_mm_fault() allocates a new page.
This behavior increases page consumption at coredump, which tend to do read-once-but-never-written page fault. This patch is for avoiding this.
Changelog: - fixed to check pte_present()/pte_none() in proper way.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Index: linux-2.6.25/mm/memory.c =================================================================== --- linux-2.6.25.orig/mm/memory.c +++ linux-2.6.25/mm/memory.c @@ -926,15 +926,15 @@ struct page *follow_page(struct vm_area_ page = NULL; pgd = pgd_offset(mm, address); if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) - goto no_page_table; + goto null_or_zeropage; pud = pud_offset(pgd, address); if (pud_none(*pud) || unlikely(pud_bad(*pud))) - goto no_page_table; + goto null_or_zeropage; pmd = pmd_offset(pud, address); if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd))) - goto no_page_table; + goto null_or_zeropage; if (pmd_huge(*pmd)) { BUG_ON(flags & FOLL_GET); @@ -947,8 +947,13 @@ struct page *follow_page(struct vm_area_ goto out; pte = *ptep; - if (!pte_present(pte)) + if (!pte_present(pte)) { + if (!(flags & FOLL_WRITE) && pte_none(pte)) { + pte_unmap_unlock(ptep, ptl); + goto null_or_zeropage; + } goto unlock; + } if ((flags & FOLL_WRITE) && !pte_write(pte)) goto unlock; page = vm_normal_page(vma, address, pte); @@ -968,7 +973,7 @@ unlock: out: return page; -no_page_table: +null_or_zeropage: /* * When core dumping an enormous anonymous area that nobody * has touched so far, we don't want to allocate page tables.
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