| Message ID | 20200513214507.30592-1-rcampbell@nvidia.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Jason Gunthorpe |
| Headers | show |
| Series | mm/hmm/test: destroy xa_array instead of looping | expand |
On Wed, May 13, 2020 at 02:45:07PM -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. Munmap() can result in a large range being > invalidated but in that case, the xa_array is likely to contain entries > that need to be invalidated. > Check for [0..ULONG_MAX] explicitly and just destroy the whole table. > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> > > 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. > > lib/test_hmm.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/lib/test_hmm.c b/lib/test_hmm.c > index 8b36c26b717b..b89852ec3c29 100644 > +++ b/lib/test_hmm.c > @@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start, > * 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. > + * However, if the entire address space is being invalidated, it > + * takes too long to clear them one at a time so destroy the array. > */ > + if (start == 0 && end == ULONG_MAX) { > + xa_destroy(&dmirror->pt); > + return; > + } > for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) > xa_erase(&dmirror->pt, pfn); > } Just use xa_for_each_range() instead of the naive loop, it already optimizes against membership and avoids the need for the xa_destroy hack Jason
On 5/15/20 4:15 PM, Jason Gunthorpe wrote: > On Wed, May 13, 2020 at 02:45:07PM -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. Munmap() can result in a large range being >> invalidated but in that case, the xa_array is likely to contain entries >> that need to be invalidated. >> Check for [0..ULONG_MAX] explicitly and just destroy the whole table. >> >> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> >> >> 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. >> >> lib/test_hmm.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/lib/test_hmm.c b/lib/test_hmm.c >> index 8b36c26b717b..b89852ec3c29 100644 >> +++ b/lib/test_hmm.c >> @@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start, >> * 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. >> + * However, if the entire address space is being invalidated, it >> + * takes too long to clear them one at a time so destroy the array. >> */ >> + if (start == 0 && end == ULONG_MAX) { >> + xa_destroy(&dmirror->pt); >> + return; >> + } >> for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) >> xa_erase(&dmirror->pt, pfn); >> } > > Just use xa_for_each_range() instead of the naive loop, it already > optimizes against membership and avoids the need for the xa_destroy > hack > > Jason > For some reason I had looked at that and rejected it but of course, it works fine. :-) Thanks!
diff --git a/lib/test_hmm.c b/lib/test_hmm.c index 8b36c26b717b..b89852ec3c29 100644 --- a/lib/test_hmm.c +++ b/lib/test_hmm.c @@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start, * 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. + * However, if the entire address space is being invalidated, it + * takes too long to clear them one at a time so destroy the array. */ + if (start == 0 && end == ULONG_MAX) { + xa_destroy(&dmirror->pt); + return; + } for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) xa_erase(&dmirror->pt, pfn); }
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. Munmap() can result in a large range being invalidated but in that case, the xa_array is likely to contain entries that need to be invalidated. Check for [0..ULONG_MAX] explicitly and just destroy the whole table. Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> --- 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. lib/test_hmm.c | 6 ++++++ 1 file changed, 6 insertions(+)