On Fri, Feb 21, 2014 at 11:23:39AM -0600, Jay Cornwall wrote: > Hi, > > I'm tracking a possible memory leak in iommu/amd. The driver uses this logic > to fault a page in response to a PRI from a device: > > npages = get_user_pages(fault->state->task, fault->state->mm, > fault->address, 1, write, 0, &page, NULL); > > if (npages == 1) > put_page(page); > else > ... > > This works correctly when get_user_pages returns a 4KB page. When > transparent huge pages are enabled any 2MB page returned by this call > appears to leak on process exit. The non-cached memory usage stays elevated > by the set of faulted 2MB pages. This behavior is not observed when the > exception handler demand faults 2MB pages. > > I notice there is a difference in reference count between the 4KB/2MB paths. > > get_user_pages (4KB): page_count()=3, page_mapcount()=1 > put_page (4KB): page_count()=2, page_mapcount()=1 > > get_user_pages (2MB): page_count()=3, page_mapcount()=1 > put_page (2MB): page_count()=3, page_mapcount()=0 > > I'm concerned that the driver appears to be holding a reference count after > put_page(). Am I interpreting this observation correctly?
Could you show output of dump_page() on 2M pages for both points? My guess is that your page is PageTail(). Refcounting for tail pages is different: on get_page() we increase *->_mapcount* of tail and increase ->_count of relevant head page. ->_count of tail pages should always be zero, but it's 3 in your case which is odd. BTW, I don't see where you take mmap_sem in drivers/iommu/amd_iommu_v2.c, which is required for gup. Do I miss something? -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
