thp: split_huge_page paging (3f04f62f) · Commits · 戴 / test

Paging logic that splits the page before it is unmapped and added to swap to ensure backwards compatibility with the legacy swap code. Eventually swap should natively pageout the hugepages to increase performance and decrease seeking and fragmentation of swap space. swapoff can just skip over huge pmd as they cannot be part of swap yet. In add_to_swap be careful to split the page only if we got a valid swap entry so we don't split hugepages with a full swap. In theory we could split pages before isolating them during the lru scan, but for khugepaged to be safe, I'm relying on either mmap_sem write mode, or PG_lock taken, so split_huge_page has to run either with mmap_sem read/write mode or PG_lock taken. Calling it from isolate_lru_page would make locking more complicated, in addition to that split_huge_page would deadlock if called by __isolate_lru_page because it has to take the lru lock to add the tail pages. Signed-off-by:

Andrea Arcangeli <aarcange@redhat.com> Acked-by:

Mel Gorman <mel@csn.ul.ie> Acked-by:

Rik van Riel <riel@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -386,6 +386,8 @@ static void collect_procs_anon(struct page page, struct list_head to_kill,
		struct task_struct *tsk;
		struct anon_vma *av;

		if (unlikely(split_huge_page(page)))
		return;
		read_lock(&tasklist_lock);
		av = page_lock_anon_vma(page);
		if (av == NULL) /* Not actually mapped anymore */

mm/rmap.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -1400,6 +1400,7 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
		int ret;

		BUG_ON(!PageLocked(page));
		BUG_ON(PageTransHuge(page));

		if (unlikely(PageKsm(page)))
		ret = try_to_unmap_ksm(page, flags);

mm/swap_state.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -157,6 +157,12 @@ int add_to_swap(struct page *page)
		if (!entry.val)
		return 0;

		if (unlikely(PageTransHuge(page)))
		if (unlikely(split_huge_page(page))) {
		swapcache_free(entry, NULL);
		return 0;
		}

		/*
		* Radix-tree node allocations from PF_MEMALLOC contexts could
		* completely exhaust the page allocator. __GFP_NOMEMALLOC

mm/swapfile.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -964,6 +964,8 @@ static inline int unuse_pmd_range(struct vm_area_struct vma, pud_t pud,
		pmd = pmd_offset(pud, addr);
		do {
		next = pmd_addr_end(addr, end);
		if (unlikely(pmd_trans_huge(*pmd)))
		continue;
		if (pmd_none_or_clear_bad(pmd))
		continue;
		ret = unuse_pte_range(vma, pmd, addr, next, entry, page);

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