From: Matthew Wilcox <willy@infradead.org>
To: linux-mm@kvack.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Hugh Dickins <hughd@google.com>, Andi Kleen <ak@linux.intel.com>
Subject: File THP and HWPoison
Date: Tue, 16 Mar 2021 14:09:47 +0000 [thread overview]
Message-ID: <20210316140947.GA3420@casper.infradead.org> (raw)
If we get a memory failure in the middle of a file THP, I think we handle
it poorly.
int memory_failure(unsigned long pfn, int flags)
...
if (TestSetPageHWPoison(p)) {
...
orig_head = hpage = compound_head(p);
...
if (PageTransHuge(hpage)) {
if (try_to_split_thp_page(p, "Memory Failure") < 0) {
action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
return -EBUSY;
}
static int try_to_split_thp_page(struct page *page, const char *msg)
{
lock_page(page);
if (!PageAnon(page) || unlikely(split_huge_page(page))) {
unsigned long pfn = page_to_pfn(page);
unlock_page(page);
if (!PageAnon(page))
pr_info("%s: %#lx: non anonymous thp\n", msg, pfn);
else
pr_info("%s: %#lx: thp split failed\n", msg, pfn);
put_page(page);
return -EBUSY;
So (for some reason) we don't even try to split a file THP. But then,
if we take a page fault on a file THP:
static struct page *next_uptodate_page(struct page *page,
...
if (PageHWPoison(page))
goto skip;
(... but we're only testing the head page here, which isn't necessarily
the one which got the error ...)
if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
vm_fault_t ret = do_set_pmd(vmf, page);
So we now map the PMD-sized page into userspace, even though it has a
HWPoison in it.
I think there are two things that we should be doing:
1. Attempt to split THPs which are file-backed. That makes most of this
problem disappear because there won't be THPs with HWPoison, mostly.
2. When the THP fails to split, use a spare page flag to indicate that
the THP contains a HWPoison bit in one of its subpages. There are a
lot of PF_SECOND flags available for this purpose.
but I know almost nothing about the memory-failure subsystem and I'm
still learning all the complexities of THPs, so it's entirely possible
I've overlooked something important.
next reply other threads:[~2021-03-16 14:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 14:09 Matthew Wilcox [this message]
2021-03-16 16:36 ` File THP and HWPoison Andi Kleen
2021-03-16 16:52 ` Matthew Wilcox
2021-03-18 14:08 ` Kirill A. Shutemov
2021-03-18 14:57 ` Matthew Wilcox
2021-03-18 17:25 ` HORIGUCHI NAOYA(堀口 直也)
2021-03-18 18:05 ` Yang Shi
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