On Tue, Nov 24, 2015 at 04:27:56PM +0100, Vlastimil Babka wrote: > On 11/13/2015 03:23 AM, Joonsoo Kim wrote: > >Now, we have tracepoint in test_pages_isolated() to notify > >pfn which cannot be isolated. But, in alloc_contig_range(), > >some error path doesn't call test_pages_isolated() so it's still > >hard to know exact pfn that causes allocation failure. > > > >This patch change this situation by calling test_pages_isolated() > >in almost error path. In allocation failure case, some overhead > >is added by this change, but, allocation failure is really rare > >event so it would not matter. > > > >In fatal signal pending case, we don't call test_pages_isolated() > >because this failure is intentional one. > > > >Signed-off-by: Joonsoo Kim <[email protected]> > >--- > > mm/page_alloc.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > >diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >index d89960d..e78d78f 100644 > >--- a/mm/page_alloc.c > >+++ b/mm/page_alloc.c > >@@ -6756,8 +6756,12 @@ int alloc_contig_range(unsigned long start, unsigned > >long end, > > if (ret) > > return ret; > > > >+ /* > >+ * In case of -EBUSY, we'd like to know which page causes problem. > >+ * So, just fall through. We will check it in test_pages_isolated(). > >+ */ > > ret = __alloc_contig_migrate_range(&cc, start, end); > >- if (ret) > >+ if (ret && ret != -EBUSY) > > goto done; > > > > /* > >@@ -6784,8 +6788,8 @@ int alloc_contig_range(unsigned long start, unsigned > >long end, > > outer_start = start; > > while (!PageBuddy(pfn_to_page(outer_start))) { > > if (++order >= MAX_ORDER) { > >- ret = -EBUSY; > >- goto done; > >+ outer_start = start; > >+ break; > > } > > outer_start &= ~0UL << order; > > } > > Ugh isn't this crazy loop broken? Shouldn't it test that the buddy > it finds has order high enough? e.g.: > buddy = pfn_to_page(outer_start) > outer_start + (1UL << page_order(buddy)) > start > > Otherwise you might end up with something like: > - at "start" there's a page that CMA failed to freed > - at "start-1" there's another non-buddy page > - at "start-3" there's an order-1 buddy, so you set outer_start to start-3 > - test_pages_isolated() will complain (via the new tracepoint) about > pfn of start-1, but actually you would like it to complain about pfn > of "start"? > > So the loop has been broken before your patch, but it didn't matter, > just potentially wasted some time by picking bogus outer_start. But > now your tracepoint will give you weird results.
Good catch. I will fix it. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
