On 04/04/2016 06:45 AM, Naoya Horiguchi wrote: > On Mon, Apr 04, 2016 at 10:39:17AM +0900, Minchan Kim wrote: >> Thanks for catching it, Vlastimil. >> It was my mistake. But in this chance, I looked over hwpoison code and >> I saw other places which increases num_poisoned_pages are successful >> migration, already freed page and successful invalidated page. >> IOW, they are already successful isolated page so I guess it should >> increase the count when only successful migration is done? > > Yes, that's right. When exiting with migration's failure, we shouldn't call > test_set_page_hwpoison or num_poisoned_pages_inc, so current code checking > (rc != -EAGAIN) is simply incorrect. Your change fixes the bug in memory > error handling. Great! Ah, I see, soft onlining works differently than I thought. >> And when I read memory_failure, it bails out without killing if it >> encounters HWPoisoned page so I think it's not for catching and >> kill the poor proces. >> >>> >>> Also (but not your fault) the put_page() preceding >>> test_set_page_hwpoison(page)) IMHO deserves a comment saying which >>> pin we are releasing and which one we still have (hopefully? if I >>> read description of da1b13ccfbebe right) otherwise it looks like >>> doing something with a page that we just potentially freed. >> >> Yes, while I read the code, I had same question. I think the releasing >> refcount is for get_any_page. > > As the other callers of page migration do, soft_offline_page expects the > migration source page to be freed at this put_page() (no pin remains.) > The refcount released here is from isolate_lru_page() in __soft_offline_page(). > (the pin by get_any_page is released by put_hwpoison_page just after it.) > > .. yes, doing something just after freeing page looks weird, but that's > how PageHWPoison flag works. IOW, many other page flags are maintained > only during one "allocate-free" life span, but PageHWPoison still does > its job beyond it. But what prevents the page from being allocated again between put_page() and test_set_page_hwpoison()? In that case we would be marking page poisoned while still in use, which is the same as marking it while still in use after a failed migration? (Also, which part prevents pages with PageHWPoison to be allocated again, anyway? I can't find it and test_set_page_hwpoison() doesn't remove from buddy freelists). Thanks. > As for commenting, this put_page() is called in any MIGRATEPAGE_SUCCESS > case (regardless of callers), so what we can say here is "we free the > source page here, bypassing LRU list" or something? > > Thanks, > Naoya Horiguchi > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>