Messages in this thread | | | Date | Wed, 30 Apr 2008 07:09:03 +0200 | From | Nick Piggin <> | Subject | Re: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression: deadlock on coredump of big process) |
| |
On Wed, Apr 30, 2008 at 08:03:33AM +0300, Mika Penttilä wrote: > 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();
Yeah, it does need to test for pte_none.
-- 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/
| |