On Tue, Sep 20, 2022 at 05:07:33PM +0800, Zhaoyang Huang wrote: > On Tue, Sep 20, 2022 at 4:55 PM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Tue, Sep 20, 2022 at 08:49:00AM +0800, zhaoyang.huang wrote: > > > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > > > > > High-order pcp page escaped from checking when both of DEBUG_VM and debug_pagealloc > > > are all disabled if it allocated again from pcp_list without going to global > > > free list, which should be introduced by 44042b4498. > > > > > > fix:44042b4498 > > > > > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > > > Why is the order check needed? In this case, I think the comment itself was > > wrong and should be corrected. free_pcp_prepare is called when dealing with > > a PCP page being freed and these days that may order-0 or high-order pages. > > Wieh DEBUG_VM disabled, the pages are checked in by bulkfree_pcp_prepare > > when freeing pages from PCP to the core allocator. Why would just > > high-order pages be checked in free_pcp_prepare and checked again in > > bulkfree_pcp_prepare? > > for high-order pcp pages(head page in fact), they might escape from > bulkfree_pcp_prepare if they were allocated from pcp-list > again(pcp->count < high) prior to going to core allocator. This is expected. The DEBUG_VM checks when enabled are more paranoid and are more likely to catch corruption or a use-after-free issue. For !DEBUG_VM, there is partial checking which is faster but leaves the possibility that a corruption of struct page will be missed. -- Mel Gorman SUSE Labs
