Messages in this thread Patch in this message | | | Date | Wed, 30 Apr 2008 14:17:38 +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 08:03:33 +0300 Mika Penttilä <mika.penttila@kolumbus.fi> wrote:
> > == > > @@ -2252,39 +2158,24 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, > > spinlock_t *ptl; > > { > > <snip> > > - page_add_new_anon_rmap(page, vma, address); > > - } else { > > - /* Map the ZERO_PAGE - vm_page_prot is readonly */ > > - page = ZERO_PAGE(address); > > - page_cache_get(page); > > - entry = mk_pte(page, vma->vm_page_prot); > > + if (unlikely(anon_vma_prepare(vma))) > > + goto oom; > > + page = alloc_zeroed_user_highpage_movable(vma, address); > > == > > > > above change is for avoiding to use ZERO_PAGE at read-page-fault to anonymous > > vma. This is reasonable I think. But at coredump, tons of read-but-never-written > > pages can be allocated. > > == > > coredump > > -> get_user_pages() > > -> follow_page() returns NULL > > -> handle mm fault > > -> do_anonymous page. > > == > > follow_page() returns ZERO_PAGE only when page table is not avaiable. > > > > So, making follow_page() return ZERO_PAGE can be a fix of extra memory > > consumpstion at core dump. (Maybe someone can think of other fix.) > > > > how about this patch ? Could you try ? > > > > (I'm sorry but I'll not be active for a week because my servers are powered off.) > > > > -Kame > > > > > > > But sure we still have to handle the fault for instance swapped pages, > for other uses of get_user_pages(); > Ah, my bad.....how about this ? I changed !pte_present() to pte_none().
-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_none() not !pte_present().
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 +947,10 @@ struct page *follow_page(struct vm_area_ goto out; pte = *ptep; - if (!pte_present(pte)) - goto unlock; + if (!(flags & FOLL_WRITE) && pte_none(pte)) { + pte_unmap_unlock(ptep, ptl); + goto null_or_zeropage; + } if ((flags & FOLL_WRITE) && !pte_write(pte)) goto unlock; page = vm_normal_page(vma, address, pte); @@ -968,7 +970,7 @@ 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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