Messages in this thread | | | Date | Fri, 19 Jun 2009 09:58:38 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 09/22] HWPOISON: Handle hardware poisoned pages in try_to_unmap |
| |
On Thu, Jun 18, 2009 at 09:31:52PM +0800, Minchan Kim wrote: > On Thu, Jun 18, 2009 at 9:14 PM, Wu Fengguang<fengguang.wu@intel.com> wrote: > > On Wed, Jun 17, 2009 at 10:03:37PM +0800, Minchan Kim wrote: > >> On Wed, Jun 17, 2009 at 10:55 PM, Wu Fengguang<fengguang.wu@intel.com> wrote: > >> > On Wed, Jun 17, 2009 at 09:44:39PM +0800, Minchan Kim wrote: > >> >> It is private mail for my question. > >> >> I don't want to make noise in LKML. > >> >> And I don't want to disturb your progress to merge HWPoison. > >> >> > >> >> > Because this race window is small enough: > >> >> > > >> >> > TestSetPageHWPoison(p); > >> >> > lock_page(page); > >> >> > try_to_unmap(page, TTU_MIGRATION|...); > >> >> > lock_page_nosync(p); > >> >> > > >> >> > such small race windows can be found all over the kernel, it's just > >> >> > insane to try to fix any of them. > >> >> > >> >> I don't know there are intentional small race windows in kernel until you said. > >> >> I thought kernel code is perfect so it wouldn't allow race window > >> >> although it is very small. But you pointed out. Until now, My thought > >> >> is wrong. > >> >> > >> >> Do you know else small race windows by intention ? > >> >> If you know it, tell me, please. It can expand my sight. :) > >> > > >> > The memory failure code does not aim to rescue 100% page corruptions. > >> > That's unreasonable goal - the kernel pages, slab pages (including the > >> > big dcache/icache) are almost impossible to isolate. > >> > > >> > Comparing to the big slab pools, the migration and other race windows are > >> > really too small to care about :) > >> > >> Also, If you will mention this contents as annotation, I will add my > >> review sign. > > > > Good suggestion. Here is a patch for comment updates. > > > >> Thanks for kind reply for my boring discussion. > > > > Boring? Not at all :) > > > > Thanks, > > Fengguang > > > > --- > > mm/memory-failure.c | 76 +++++++++++++++++++++++++----------------- > > 1 file changed, 47 insertions(+), 29 deletions(-) > > > > --- sound-2.6.orig/mm/memory-failure.c > > +++ sound-2.6/mm/memory-failure.c > > @@ -1,4 +1,8 @@ > > /* > > + * linux/mm/memory-failure.c > > + * > > + * High level machine check handler. > > + * > > * Copyright (C) 2008, 2009 Intel Corporation > > * Authors: Andi Kleen, Fengguang Wu > > * > > @@ -6,29 +10,36 @@ > > * the GNU General Public License ("GPL") version 2 only as published by the > > * Free Software Foundation. > > * > > - * High level machine check handler. Handles pages reported by the > > - * hardware as being corrupted usually due to a 2bit ECC memory or cache > > - * failure. > > - * > > - * This focuses on pages detected as corrupted in the background. > > - * When the current CPU tries to consume corruption the currently > > - * running process can just be killed directly instead. This implies > > - * that if the error cannot be handled for some reason it's safe to > > - * just ignore it because no corruption has been consumed yet. Instead > > - * when that happens another machine check will happen. > > - * > > - * Handles page cache pages in various states. The tricky part > > - * here is that we can access any page asynchronous to other VM > > - * users, because memory failures could happen anytime and anywhere, > > - * possibly violating some of their assumptions. This is why this code > > - * has to be extremely careful. Generally it tries to use normal locking > > - * rules, as in get the standard locks, even if that means the > > - * error handling takes potentially a long time. > > - * > > - * The operation to map back from RMAP chains to processes has to walk > > - * the complete process list and has non linear complexity with the number > > - * mappings. In short it can be quite slow. But since memory corruptions > > - * are rare we hope to get away with this. > > + * Pages are reported by the hardware as being corrupted usually due to a > > + * 2bit ECC memory or cache failure. Machine check can either be raised when > > + * corruption is found in background memory scrubbing, or when someone tries to > > + * consume the corruption. This code focuses on the former case. If it cannot > > + * handle the error for some reason it's safe to just ignore it because no > > + * corruption has been consumed yet. Instead when that happens another (deadly) > > + * machine check will happen. > > + * > > + * The tricky part here is that we can access any page asynchronous to other VM > > + * users, because memory failures could happen anytime and anywhere, possibly > > + * violating some of their assumptions. This is why this code has to be > > + * extremely careful. Generally it tries to use normal locking rules, as in get > > + * the standard locks, even if that means the error handling takes potentially > > + * a long time. > > + * > > + * We don't aim to rescue 100% corruptions. That's unreasonable goal - the > > + * kernel text and slab pages (including the big dcache/icache) are almost > > + * impossible to isolate. We also try to keep the code clean by ignoring the > > + * other thousands of small corruption windows. > > other thousands of small corruption windows(ex, migration, ...) > As far as you know , please write down them.
Like this:
new_page = alloc_page(); <small corruption window> write to new_page <small corruption window> read from new_page
> Anyway, I already added my sign. > Thanks for your effort never get exhausted. :)
You are welcome :)
Thanks, Fengguang -- 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/
| |