19 Jun 2013 08:44
[PATCH] powerpc/THP: Wait for all hash_page calls to finish before invalidating HPTE entries
Aneesh Kumar K.V <aneesh.kumar <at> linux.vnet.ibm.com>
2013-06-19 06:44:54 GMT
2013-06-19 06:44:54 GMT
From: "Aneesh Kumar K.V" <aneesh.kumar <at> linux.vnet.ibm.com> When we collapse normal pages to hugepage, we first clear the pmd, then invalidate all the PTE entries. The assumption here is that any low level page fault will see pmd as none and take the slow path that will wait on mmap_sem. But we could very well be in a hash_page with local ptep pointer value. Such a hash page can result in adding new HPTE entries for normal subpages/small page. That means we could be modifying the page content as we copy them to a huge page. Fix this by waiting on hash_page to finish after marking the pmd none and bfore invalidating HPTE entries. We use the heavy kick_all_cpus_sync(). This should be ok as we do this in the background khugepaged thread and not in application context. But we block page fault handling for this time. Also if we find collapse slow we can ideally increase the scan rate. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar <at> linux.vnet.ibm.com> --- arch/powerpc/mm/pgtable_64.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c index bbecac4..4bb44c3 100644 --- a/arch/powerpc/mm/pgtable_64.c +++ b/arch/powerpc/mm/pgtable_64.c <at> <at> -543,6 +543,14 <at> <at> pmd_t pmdp_clear_flush(struct vm_area_struct *vma, unsigned long address, pmd = *pmdp; pmd_clear(pmdp); /* + * Wait for all pending hash_page to finish + * We can do this by waiting for a context switch to happen on + * the cpus. Any new hash_page after this will see pmd none + * and fallback to code that takes mmap_sem and hence will block(Continue reading)
>
> > - We already have an EEH thread, why not just use it ? IE send it a special
> >type of message that makes it query the backend for error info instead ?
> >
>
> Ok. I'll try to do as you suggested in next revision. Something like:
>
> - Interrupt comes in
> - OPAL notifier callback
> - Mark all PHB and its subordinate PEs "isolated" since we don't know
> which PHB/PE has problems (Note: we still need eeh_serialize_lock())
No, don't mark anything. It wouldn't be good to start marking "isolated"
things that aren't. It doesn't matter if we don't "know" they are
isolated just yet. Just "poke" the EEH thread with a different type of
message from the current one.
> - Create an EEH event without binding PE to EEH core.
> - EEH core starts new kthread and calls to next_error() backend
> and handle the EEH errors accordingly.
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