2020-05-16 01:09:25

by Ralph Campbell

Subject: [PATCH v2] mm/hmm/test: use xa_for_each_range instead of looping

The test driver uses an xa_array to store virtual to physical address
translations for a simulated hardware device. The MMU notifier
invalidation callback is used to keep the table consistent with the CPU
page table and is frequently called only for a page or two. However, if
the test process exits unexpectedly or is killed, the range can be
[0..ULONG_MAX] in which case calling xa_erase() for every possible PFN
results in CPU timeouts.
Use xa_for_each_range() to efficiently erase entries in the range.

Signed-off-by: Ralph Campbell <[email protected]>
---

This patch is based on Jason Gunthorpe's hmm tree and should be folded
into the ("mm/hmm/test: add selftest driver for HMM") patch once this
patch is reviewed, etc.

v1 -> v2:
Use xa_for_each_range() instead of special casing [0..ULONG_MAX].

lib/test_hmm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 8b36c26b717b..5c1858e325ba 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -196,13 +196,15 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
unsigned long end)
{
unsigned long pfn;
+ void *entry;

/*
* The XArray doesn't hold references to pages since it relies on
* the mmu notifier to clear page pointers when they become stale.
* Therefore, it is OK to just clear the entry.
*/
- for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++)
+ xa_for_each_range(&dmirror->pt, pfn, entry, start >> PAGE_SHIFT,
+ end >> PAGE_SHIFT)
xa_erase(&dmirror->pt, pfn);
}

--
2.20.1

2020-05-19 19:53:05

by Jason Gunthorpe

Subject: Re: [PATCH v2] mm/hmm/test: use xa_for_each_range instead of looping

On Fri, May 15, 2020 at 06:04:24PM -0700, Ralph Campbell wrote:
> The test driver uses an xa_array to store virtual to physical address
> translations for a simulated hardware device. The MMU notifier
> invalidation callback is used to keep the table consistent with the CPU
> page table and is frequently called only for a page or two. However, if
> the test process exits unexpectedly or is killed, the range can be
> [0..ULONG_MAX] in which case calling xa_erase() for every possible PFN
> results in CPU timeouts.
> Use xa_for_each_range() to efficiently erase entries in the range.
>
> Signed-off-by: Ralph Campbell <[email protected]>
> ---
>
> This patch is based on Jason Gunthorpe's hmm tree and should be folded
> into the ("mm/hmm/test: add selftest driver for HMM") patch once this
> patch is reviewed, etc.
>
> v1 -> v2:
> Use xa_for_each_range() instead of special casing [0..ULONG_MAX].
>
> lib/test_hmm.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

I squashed this in

Thanks,
Jason