On Wed, May 13, 2020, 2:36 AM Qian Cai <cai@xxxxxx> wrote:
Put zswap z3fold pages into the memory and then offline those memory would trigger an infinite loop here in
__offline_pages() --> do_migrate_range() because there is no error handling,
if (pfn) {
/*
* TODO: fatal migration failures should bail
* out
*/
do_migrate_range(pfn, end_pfn);
There, isolate_movable_page() will always return -EBUSY because,
if (!mapping->a_ops->isolate_page(page, mode))
goto out_no_isolated;
i.e., z3fold_page_isolate() will always return false because,
zhdr->mapped_count == 2
So who mapped these pages? The whole zswap operation presumes that objects are mapped for a short while to run some I/O and so, most of the time zhdr->mapped_count would be 0.
Removing that check in ->isolate() is not a big deal, but ->migratepage() shall not allow actual migration anyway if there are mapped objects.
~Vitaly
