[PATCH v2 2/5] mm/swapin: Retry swapin by VMA lock if the lock was released for I/O

[Barry Song (Xiaomi)]

If the current do_swap_page() took the per-VMA lock and we dropped it only
to wait for I/O completion (e.g., use folio_wait_locked()), then when
do_swap_page() is retried after the I/O completes, it should still qualify
for the per-VMA-lock path.

Tested-by: Wang Lian <wanglian at kylinos.cn>
Tested-by: Kunwu Chan <chentao at kylinos.cn>
Reviewed-by: Wang Lian <lianux.mm at gmail.com>
Reviewed-by: Kunwu Chan <kunwu.chan at gmail.com>
Signed-off-by: Barry Song (Xiaomi) <baohua at kernel.org>
---
 mm/memory.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 199214f8de08..00ee1599d637 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4791,6 +4791,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	unsigned long page_idx;
 	unsigned long address;
 	pte_t *ptep;
+	bool retry_by_vma_lock = false;
 
 	if (!pte_unmap_same(vmf))
 		goto out;
@@ -4896,8 +4897,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	swapcache = folio;
 	ret |= folio_lock_or_retry(folio, vmf);
-	if (ret & VM_FAULT_RETRY)
+	if (ret & VM_FAULT_RETRY) {
+		if (fault_flag_allow_retry_first(vmf->flags) &&
+		    !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT) &&
+		    (vmf->flags & FAULT_FLAG_VMA_LOCK))
+			retry_by_vma_lock = true;
 		goto out_release;
+	}
 
 	page = folio_file_page(folio, swp_offset(entry));
 	/*
@@ -5182,7 +5188,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	}
 	if (si)
 		put_swap_device(si);
-	return ret;
+	return ret | (retry_by_vma_lock ? VM_FAULT_RETRY_VMA : 0);
 }
 
 static bool pte_range_none(pte_t *pte, int nr_pages)
-- 
2.39.3 (Apple Git-146)