Messages in this thread Patch in this message | | | Date | Mon, 15 Jun 2009 03:57:49 +0300 | From | Izik Eidus <> | Subject | Re: [PATCH 0/3] ksm: write protect pages from inside ksm |
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On Mon, 15 Jun 2009 03:05:14 +0300 Izik Eidus <ieidus@redhat.com> wrote:
> Izik Eidus wrote: > > Izik Eidus wrote: > >> Hugh Dickins wrote: > >>> On Sat, 13 Jun 2009, Izik Eidus wrote: > >>> > >>>> Hugh, so untill here we are sync, > >>>> > >>> > >>> Yes, that fits with what I have here, thanks (or where it didn't > >>> quite fit, e.g. ' versus `, I've adjusted to what you have!). And > >>> thanks for fixing my *orig_pte = *ptep bug, you did point that out > >>> before, but I misunderstood at first. > >>> > >>> > >>>> Question is what you want me to do now?, > >>>> (Beacuse we are skipping 2.6.31, It is ok to you to tell me > >>>> something like: "Shut up and let me see what i can get with this > >>>> madvise" - that from one side. > >>>> From another side if you want me to do anything please say. > >>>> > >>> > >>> I had to get a bit further at my end before answering on that, > >>> but now the answer is clear: please do some testing of your RFC > >>> madvise() version (which is what I'm just tidying up a little), > >>> and let me know any bugfixes you find. Try with SLAB or SLUB or > >>> SLQB debug on e.g. CONFIG_SLUB=y, CONFIG_SLUB_DEBUG=y and boot > >>> option "slub_debug". > >>> > >> > >> Sure, let me check it. > >> (You do have Andrea patch that fix the "used after free slab > >> entries" ?) > > > > How fast is it crush opps to you?, I compiled it and ran it here on > > 2.6.30-rc4-mm1 with: > > "Enable SLQB debugging support" and "SLQB debugging on by default, > > and it run and merge (i am using qemu processes to run virtual > > machines to merge the pages between them) > > > > ("SLQB debugging on by defaul" mean i dont have to add boot > > pareameter right?) > > > > Maybe i should try update into newer version of the mm tree? (last > > commit here is Jul 22) > > OK, bug on my side, just got that oppss, will try to fix and send > patch. > > (Sorry for the noise) > > > > >> > >>> I'm finding, whether with your RFC or my tidyup, that kksmd > >>> soon oopses in get_next_mmlist (or perhaps find_vma): presumably > >>> accessing a vma or mm which already got freed (if you don't have > >>> slab debugging on, it's liable to hang instead). > >>> > >>> (I've also not seen it actually merging yet: if you register > >>> or madvise a large anon area and memset it, the /dev/ksm version > >>> would merge all its pages, but I've not seen the madvise version > >>> do so yet - though maybe there's something stupidly wrong in my > >>> testing, really I'm more worried about the oopses at present.) > >>> > >>> Note that mmotm includes a patch of Nick's which adds a function > >>> madvise_behavior_valid() - you'll need to add your MADVs into its > >>> list to get it to work at all there. > >>> > >>> Here's a patch I added a month or so ago, when trying to > >>> experiment with KSM on all mms: shouldn't be necessary if your mm > >>> refcounting is right, but might help to avoid extra weirdness > >>> when things go wrong: exit_mmap() leaves stale vma pointers > >>> around, reckoning that nobody can be interested by now; but maybe > >>> KSM might peep so better to tidy them up at least while > >>> debugging... > >>> > >>> Thanks, > >>> Hugh > >>> > >>> --- old/mm/mmap.c 2009-05-01 13:47:45.000000000 +0100 > >>> +++ new/mm/mmap.c 2009-05-03 11:34:47.000000000 +0100 > >>> @@ -2112,6 +2112,14 @@ void exit_mmap(struct mm_struct *mm) > >>> tlb_finish_mmu(tlb, 0, end); > >>> > >>> /* > >>> + * Make sure get_user_pages() and find_vma() etc. will find > >>> nothing: > >>> + * this may be necessary for KSM. > >>> + */ > >>> + mm->mmap = NULL; > >>> + mm->mmap_cache = NULL; > >>> + mm->mm_rb = RB_ROOT; > >>> + > >>> + /* > >>> * Walk the list again, actually closing and freeing it, > >>> * with preemption enabled, without holding any MM locks. > >>> */ > >>> > >> > >> > > > > > >
Ok, below is ugly fix for the opss..
From 3be1ad5a9f990113e8849fa1e74c4e74066af131 Mon Sep 17 00:00:00 2001 From: Izik Eidus <ieidus@redhat.com> Date: Mon, 15 Jun 2009 03:52:05 +0300 Subject: [PATCH] ksm: madvise-rfc: really ugly fix for the oppss bug.
This patch is just so it can run without to crush with the madvise rfc patch.
True fix for this i think is adding another list for ksm inside the mm struct. In the meanwhile i will try to think about other way how to fix this bug.
Hugh, i hope at least now you will be able to run it without it will crush to you.
Signed-off-by: Izik Eidus <ieidus@redhat.com> --- kernel/fork.c | 11 ++++++----- 1 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c index e5ef58c..771b89a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -484,17 +484,18 @@ void mmput(struct mm_struct *mm) { might_sleep(); + spin_lock(&mmlist_lock); if (atomic_dec_and_test(&mm->mm_users)) { + if (!list_empty(&mm->mmlist)) + list_del(&mm->mmlist); + spin_unlock(&mmlist_lock); exit_aio(mm); exit_mmap(mm); set_mm_exe_file(mm, NULL); - if (!list_empty(&mm->mmlist)) { - spin_lock(&mmlist_lock); - list_del(&mm->mmlist); - spin_unlock(&mmlist_lock); - } put_swap_token(mm); mmdrop(mm); + } else { + spin_unlock(&mmlist_lock); } } EXPORT_SYMBOL_GPL(mmput); -- 1.5.6.5
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