Commit 4d928e20 authored by Miaohe Lin's avatar Miaohe Lin Committed by Andrew Morton
Browse files

mm/khugepaged: stop swapping in page when VM_FAULT_RETRY occurs 

When do_swap_page returns VM_FAULT_RETRY, we do not retry here and thus
swap entry will remain in pagetable.  This will result in later failure. 
So stop swapping in pages in this case to save cpu cycles.  As A further
optimization, mmap_lock is released when __collapse_huge_page_swapin()
fails to avoid relocking mmap_lock.  And "swapped_in++" is moved after
error handling to make it more accurate.

Link: https://lkml.kernel.org/r/20220625092816.4856-3-linmiaohe@huawei.com


Signed-off-by: default avatarMiaohe Lin <linmiaohe@huawei.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent dd5ff79d

mm/khugepaged.c

+14 −18
Original line number Diff line number Diff line
@@ -972,8 +972,8 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, 
 * Bring missing pages in from swap, to complete THP collapse.

 * Only done if khugepaged_scan_pmd believes it is worthwhile.

 *

 * Called and returns without pte mapped or spinlocks held,

 * but with mmap_lock held to protect against vma changes.

 * Called and returns without pte mapped or spinlocks held.

 * Note that if false is returned, mmap_lock will be released.

 */



static bool __collapse_huge_page_swapin(struct mm_struct *mm,
@@ -1000,27 +1000,24 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, 
			pte_unmap(vmf.pte);

			continue;

		}

		swapped_in++;

		ret = do_swap_page(&vmf);



		/* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */

		/*

		 * do_swap_page returns VM_FAULT_RETRY with released mmap_lock.

		 * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because

		 * we do not retry here and swap entry will remain in pagetable

		 * resulting in later failure.

		 */

		if (ret & VM_FAULT_RETRY) {

			mmap_read_lock(mm);

			if (hugepage_vma_revalidate(mm, haddr, &vma)) {

				/* vma is no longer available, don't continue to swapin */

				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);

				return false;

			}

			/* check if the pmd is still valid */

			if (mm_find_pmd(mm, haddr) != pmd) {

			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);

			return false;

		}

		}

		if (ret & VM_FAULT_ERROR) {

			mmap_read_unlock(mm);

			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);

			return false;

		}

		swapped_in++;

	}



	/* Drain LRU add pagevec to remove extra pin on the swapped in pages */
@@ -1086,13 +1083,12 @@ static void collapse_huge_page(struct mm_struct *mm, 
	}



	/*

	 * __collapse_huge_page_swapin always returns with mmap_lock locked.

	 * If it fails, we release mmap_lock and jump out_nolock.

	 * __collapse_huge_page_swapin will return with mmap_lock released

	 * when it fails. So we jump out_nolock directly in that case.

	 * Continuing to collapse causes inconsistency.

	 */

	if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,

						     pmd, referenced)) {

		mmap_read_unlock(mm);

		goto out_nolock;

	}