Messages in this thread | | | Date | Wed, 30 Apr 2008 08:03:33 +0300 | From | Mika Penttilä <> | Subject | Re: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression: deadlock on coredump of big process) |
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KAMEZAWA Hiroyuki wrote: > On Tue, 29 Apr 2008 10:10:58 -0400 > Tony Battersby <tonyb@cybernetics.com> wrote: > >> If I leave more memory free by changing the argument to >> malloc_all_but_x_mb(), then I have to increase the number of threads >> required to trigger the deadlock. Changing the thread stack size via >> setrlimit(RLIMIT_STACK) also changes the number of threads that are >> required to trigger the deadlock. For example, with >> malloc_all_but_x_mb(16) and the default stack size of 8 MB, <= 5 threads >> will coredump successfully, and >= 6 threads will deadlock. With >> malloc_all_but_x_mb(16) and a reduced stack size of 4096 bytes, <= 8 >> threads will coredump successfully, and >= 9 threads will deadlock. >> >> Also note that the "free" command reports 10 MB free memory while the >> program is running before the segfault is triggered. >> >> > Hmm, my idea is below. > > Nick's remove ZERO_PAGE patch includes following change > > == > @@ -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();
--Mika
> == > follow_page() returns ZERO_PAGE if page table is not available. > but returns NULL pte is not presentl. > > 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_present(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. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > >
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