[PATCH v2 8/9] mm/swap: introduce a helper for swapin without vmfault

[Kairui Song]

From: Kairui Song <kasong@xxxxxxxxxxx>

There are two places where swapin is not caused by direct anon page fault:
- shmem swapin, invoked indirectly through shmem mapping
- swapoff

They used to construct a pseudo vmfault struct for swapin function.
Shmem has dropped the pseudo vmfault recently in commit ddc1a5cbc05d
("mempolicy: alloc_pages_mpol() for NUMA policy without vma"). Swapoff
path is still using one.

Introduce a helper for them both, this help save stack usage for swapoff
path, and help apply a unified swapin cache and readahead policy check.

Due to missing vmfault info, the caller have to pass in mempolicy
explicitly, make it different from swapin_entry and name it
swapin_entry_mpol.

This commit convert swapoff to use this helper, follow-up commits will
convert shmem to use it too.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/swap.h       |  9 +++++++++
 mm/swap_state.c | 40 ++++++++++++++++++++++++++++++++--------
 mm/swapfile.c   | 15 ++++++---------
 3 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/mm/swap.h b/mm/swap.h
index 9180411afcfe..8f790a67b948 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -73,6 +73,9 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
 		struct mempolicy *mpol, pgoff_t ilx);
 struct folio *swapin_entry(swp_entry_t entry, gfp_t flag,
 			    struct vm_fault *vmf, enum swap_cache_result *result);
+struct folio *swapin_entry_mpol(swp_entry_t entry, gfp_t gfp_mask,
+				struct mempolicy *mpol, pgoff_t ilx,
+				enum swap_cache_result *result);
 
 static inline unsigned int folio_swap_flags(struct folio *folio)
 {
@@ -109,6 +112,12 @@ static inline struct folio *swapin_entry(swp_entry_t swp, gfp_t gfp_mask,
 	return NULL;
 }
 
+static inline struct page *swapin_entry_mpol(swp_entry_t entry, gfp_t gfp_mask,
+		struct mempolicy *mpol, pgoff_t ilx, enum swap_cache_result *result)
+{
+	return NULL;
+}
+
 static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
 {
 	return 0;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 21badd4f0fc7..3edf4b63158d 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -880,14 +880,13 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
  * in.
  */
 static struct folio *swapin_direct(swp_entry_t entry, gfp_t gfp_mask,
-				  struct vm_fault *vmf, void *shadow)
+				   struct mempolicy *mpol, pgoff_t ilx,
+				   void *shadow)
 {
-	struct vm_area_struct *vma = vmf->vma;
 	struct folio *folio;
 
-	/* skip swapcache */
-	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
-				vma, vmf->address, false);
+	folio = (struct folio *)alloc_pages_mpol(gfp_mask, 0,
+			mpol, ilx, numa_node_id());
 	if (folio) {
 		if (mem_cgroup_swapin_charge_folio(folio, NULL,
 						   GFP_KERNEL, entry)) {
@@ -943,18 +942,18 @@ struct folio *swapin_entry(swp_entry_t entry, gfp_t gfp_mask,
 		goto done;
 	}
 
+	mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
 	if (swap_use_no_readahead(swp_swap_info(entry), entry)) {
-		folio = swapin_direct(entry, gfp_mask, vmf, shadow);
+		folio = swapin_direct(entry, gfp_mask, mpol, ilx, shadow);
 		cache_result = SWAP_CACHE_BYPASS;
 	} else {
-		mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
 		if (swap_use_vma_readahead())
 			folio = swap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf);
 		else
 			folio = swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
-		mpol_cond_put(mpol);
 		cache_result = SWAP_CACHE_MISS;
 	}
+	mpol_cond_put(mpol);
 done:
 	if (result)
 		*result = cache_result;
@@ -962,6 +961,31 @@ struct folio *swapin_entry(swp_entry_t entry, gfp_t gfp_mask,
 	return folio;
 }
 
+struct folio *swapin_entry_mpol(swp_entry_t entry, gfp_t gfp_mask,
+				struct mempolicy *mpol, pgoff_t ilx,
+				enum swap_cache_result *result)
+{
+	enum swap_cache_result cache_result;
+	void *shadow = NULL;
+	struct folio *folio;
+
+	folio = swap_cache_get_folio(entry, NULL, 0, &shadow);
+	if (folio) {
+		cache_result = SWAP_CACHE_HIT;
+	} else if (swap_use_no_readahead(swp_swap_info(entry), entry)) {
+		folio = swapin_direct(entry, gfp_mask, mpol, ilx, shadow);
+		cache_result = SWAP_CACHE_BYPASS;
+	} else {
+		folio = swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
+		cache_result = SWAP_CACHE_MISS;
+	}
+
+	if (result)
+		*result = cache_result;
+
+	return folio;
+}
+
 #ifdef CONFIG_SYSFS
 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
 				     struct kobj_attribute *attr, char *buf)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5aa44de11edc..2f77bf143af8 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1840,18 +1840,13 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 	do {
 		struct folio *folio;
 		unsigned long offset;
+		struct mempolicy *mpol;
 		unsigned char swp_count;
 		swp_entry_t entry;
+		pgoff_t ilx;
 		int ret;
 		pte_t ptent;
 
-		struct vm_fault vmf = {
-			.vma = vma,
-			.address = addr,
-			.real_address = addr,
-			.pmd = pmd,
-		};
-
 		if (!pte++) {
 			pte = pte_offset_map(pmd, addr);
 			if (!pte)
@@ -1871,8 +1866,10 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		pte_unmap(pte);
 		pte = NULL;
 
-		folio = swapin_entry(entry, GFP_HIGHUSER_MOVABLE,
-				     &vmf, NULL);
+		mpol = get_vma_policy(vma, addr, 0, &ilx);
+		folio = swapin_entry_mpol(entry, GFP_HIGHUSER_MOVABLE,
+					  mpol, ilx, NULL);
+		mpol_cond_put(mpol);
 		if (!folio) {
 			/*
 			 * The entry could have been freed, and will not
-- 
2.43.0