Hi Kirill,
On Tue, Jul 14, 2020 at 10:33:06AM +0300, Kirill A. Shutemov wrote:
On Sun, Jul 12, 2020 at 03:58:06PM -0700, Linus Torvalds wrote:
Anybody else have any opinions?
Maybe we just shouldn't allow move_normal_pmd() if ranges overlap?
Other option: pass 'overlaps' down to move_normal_pmd() and only WARN() if see establised PMD without overlaps being true.
I was thinking we should not call move_page_tables() with overlapping ranges at all, just to keep things simple. I am concerned about other issues such as if you move a range forward, you will end up overwriting part of the source range.
Allow me some time to develop a proper patch, I have it on my list. I will try to get to it this week.
I think we can also add a patch to detect the overlap as you did and warn in such situation.
Thoughts?
thanks,
- Joel
Untested patch:
diff --git a/mm/mremap.c b/mm/mremap.c index 5dd572d57ca9..e33fcee541fe 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -245,6 +245,18 @@ unsigned long move_page_tables(struct vm_area_struct *vma, unsigned long extent, next, old_end; struct mmu_notifier_range range; pmd_t *old_pmd, *new_pmd;
- bool overlaps;
- /*
* shift_arg_pages() can call move_page_tables() on overlapping ranges.* In this case we cannot use move_normal_pmd() because destination pmd* might be established page table: move_ptes() doesn't free page* table.*/- if (old_addr > new_addr)
overlaps = old_addr - new_addr < len;- else
overlaps = new_addr - old_addr < len;old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end); @@ -282,7 +294,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma, split_huge_pmd(vma, old_pmd, old_addr); if (pmd_trans_unstable(old_pmd)) continue;
} else if (extent == PMD_SIZE) {
} else if (!overlaps && extent == PMD_SIZE) {#ifdef CONFIG_HAVE_MOVE_PMD /* * If the extent is PMD-sized, try to speed the move by -- Kirill A. Shutemov