Messages in this thread | | | Date | Tue, 1 Sep 2009 14:46:52 +0800 | From | Wu Fengguang <> | Subject | Re: [RFC][PATCH 0/4] memcg: add support for hwpoison testing |
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On Tue, Sep 01, 2009 at 10:32:14AM +0800, KAMEZAWA Hiroyuki wrote: > On Tue, 1 Sep 2009 10:25:14 +0800 > Wu Fengguang <fengguang.wu@intel.com> wrote: > > > 4. I can't understand why you need this. I wonder you can get pfn via > > > /proc/<pid>/????. And this may insert HWPOISON to page-cache of shared > > > library and "unexpected" process will be poisoned. > > > > Sorry I should have explained this. It's mainly for correctness. > > When a user space tool queries the task PFNs in /proc/pid/pagemap and > > then send to /debug/hwpoison/corrupt-pfn, there is a racy window that > > the page could be reclaimed and allocated by some one else. It would > > be awkward to try to pin the pages in user space. So we need the > > guarantees provided by /debug/hwpoison/corrupt-filter-memcg, which > > will be checked inside the page lock with elevated reference count. > > > > memcg never holds refcnt for a page and the kernel::vmscan.c can reclaim > any pages under memcg whithout checking anything related to memcg. > *And*, your code has no "pin" code. > This patch sed does no jobs for your concern.
We grabbed page here, which is not in the scope of this patchset:
static int try_memory_failure(unsigned long pfn) { struct page *p; int res = -EINVAL;
if (!pfn_valid(pfn)) return res;
p = pfn_to_page(pfn); if (!get_page_unless_zero(compound_head(p))) return res;
lock_page_nosync(compound_head(p));
if (hwpoison_filter(p)) goto out;
res = __memory_failure(pfn, 18, MEMORY_FAILURE_FLAG_COUNTED | MEMORY_FAILURE_FLAG_LOCKED); out: unlock_page(p); return res; }
> I recommend you to add > /debug/hwpoizon/pin-pfn > > Then, > echo pfn > /debug/hwpoizon/pin-pfn > # add pfn for hwpoison debug's watch list. and elevate refcnt > check 'pfn' is still used. > echo pfn > /debug/hwpoison/corrupt-pfn > # check 'watch list' and make it corrupt and release refcnt. > or some.
Looks like a good alternative. At least no more memcg dependency..
Cheers, Fengguang
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