shmem: move memcg charge out of shmem_add_to_page_cache()

Extract shmem's memcg charging out of shmem_add_to_page_cache(): it's
misleading done there, because many calls are dealing with a swapcache
page, whose memcg is nowadays always remembered while swapped out, then
the charge re-levied when it's brought back into swapcache.

Temporarily move it back up to the shmem_get_folio_gfp() level, where the
memcg was charged before v5.8; but the next commit goes on to move it back
down to a new home.

In making this change, it becomes clear that shmem_swapin_folio() does not
need to know the vma, just the fault mm (if any): call it fault_mm rather
than charge_mm - let mem_cgroup_charge() decide whom to charge.

Link: https://lkml.kernel.org/r/4b2143c5-bf32-64f0-841-81a81158dac@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Carlos Maiolino <cem@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index fabce18ed9e5cf1ca3b4ee02bef6c9fcca110849..670f77de3238084a04761d908cb63870c757be1a 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -146,9 +146,8 @@ static unsigned long shmem_default_max_inodes(void)
 #endif
 
 static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
-                            struct folio **foliop, enum sgp_type sgp,
-                            gfp_t gfp, struct vm_area_struct *vma,
-                            vm_fault_t *fault_type);
+                       struct folio **foliop, enum sgp_type sgp, gfp_t gfp,
+                       struct mm_struct *fault_mm, vm_fault_t *fault_type);
 
 static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
 {
@@ -760,12 +759,10 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
  */
 static int shmem_add_to_page_cache(struct folio *folio,
                                   struct address_space *mapping,
-                                  pgoff_t index, void *expected, gfp_t gfp,
-                                  struct mm_struct *charge_mm)
+                                  pgoff_t index, void *expected, gfp_t gfp)
 {
        XA_STATE_ORDER(xas, &mapping->i_pages, index, folio_order(folio));
        long nr = folio_nr_pages(folio);
-       int error;
 
        VM_BUG_ON_FOLIO(index != round_down(index, nr), folio);
        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
@@ -776,16 +773,7 @@ static int shmem_add_to_page_cache(struct folio *folio,
        folio->mapping = mapping;
        folio->index = index;
 
-       if (!folio_test_swapcache(folio)) {
-               error = mem_cgroup_charge(folio, charge_mm, gfp);
-               if (error) {
-                       if (folio_test_pmd_mappable(folio)) {
-                               count_vm_event(THP_FILE_FALLBACK);
-                               count_vm_event(THP_FILE_FALLBACK_CHARGE);
-                       }
-                       goto error;
-               }
-       }
+       gfp &= GFP_RECLAIM_MASK;
        folio_throttle_swaprate(folio, gfp);
 
        do {
@@ -813,15 +801,12 @@ unlock:
        } while (xas_nomem(&xas, gfp));
 
        if (xas_error(&xas)) {
-               error = xas_error(&xas);
-               goto error;
+               folio->mapping = NULL;
+               folio_ref_sub(folio, nr);
+               return xas_error(&xas);
        }
 
        return 0;
-error:
-       folio->mapping = NULL;
-       folio_ref_sub(folio, nr);
-       return error;
 }
 
 /*
@@ -1324,10 +1309,8 @@ static int shmem_unuse_swap_entries(struct inode *inode,
 
                if (!xa_is_value(folio))
                        continue;
-               error = shmem_swapin_folio(inode, indices[i],
-                                         &folio, SGP_CACHE,
-                                         mapping_gfp_mask(mapping),
-                                         NULL, NULL);
+               error = shmem_swapin_folio(inode, indices[i], &folio, SGP_CACHE,
+                                       mapping_gfp_mask(mapping), NULL, NULL);
                if (error == 0) {
                        folio_unlock(folio);
                        folio_put(folio);
@@ -1810,12 +1793,11 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
  */
 static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
                             struct folio **foliop, enum sgp_type sgp,
-                            gfp_t gfp, struct vm_area_struct *vma,
+                            gfp_t gfp, struct mm_struct *fault_mm,
                             vm_fault_t *fault_type)
 {
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
-       struct mm_struct *charge_mm = vma ? vma->vm_mm : NULL;
        struct swap_info_struct *si;
        struct folio *folio = NULL;
        swp_entry_t swap;
@@ -1843,7 +1825,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
                if (fault_type) {
                        *fault_type |= VM_FAULT_MAJOR;
                        count_vm_event(PGMAJFAULT);
-                       count_memcg_event_mm(charge_mm, PGMAJFAULT);
+                       count_memcg_event_mm(fault_mm, PGMAJFAULT);
                }
                /* Here we actually start the io */
                folio = shmem_swapin(swap, gfp, info, index);
@@ -1880,8 +1862,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
        }
 
        error = shmem_add_to_page_cache(folio, mapping, index,
-                                       swp_to_radix_entry(swap), gfp,
-                                       charge_mm);
+                                       swp_to_radix_entry(swap), gfp);
        if (error)
                goto failed;
 
@@ -1929,7 +1910,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
        struct address_space *mapping = inode->i_mapping;
        struct shmem_inode_info *info = SHMEM_I(inode);
        struct shmem_sb_info *sbinfo;
-       struct mm_struct *charge_mm;
+       struct mm_struct *fault_mm;
        struct folio *folio;
        pgoff_t hindex;
        gfp_t huge_gfp;
@@ -1946,7 +1927,7 @@ repeat:
        }
 
        sbinfo = SHMEM_SB(inode->i_sb);
-       charge_mm = vma ? vma->vm_mm : NULL;
+       fault_mm = vma ? vma->vm_mm : NULL;
 
        folio = filemap_get_entry(mapping, index);
        if (folio && vma && userfaultfd_minor(vma)) {
@@ -1958,7 +1939,7 @@ repeat:
 
        if (xa_is_value(folio)) {
                error = shmem_swapin_folio(inode, index, &folio,
-                                         sgp, gfp, vma, fault_type);
+                                          sgp, gfp, fault_mm, fault_type);
                if (error == -EEXIST)
                        goto repeat;
 
@@ -2044,9 +2025,16 @@ alloc_nohuge:
        if (sgp == SGP_WRITE)
                __folio_set_referenced(folio);
 
-       error = shmem_add_to_page_cache(folio, mapping, hindex,
-                                       NULL, gfp & GFP_RECLAIM_MASK,
-                                       charge_mm);
+       error = mem_cgroup_charge(folio, fault_mm, gfp);
+       if (error) {
+               if (folio_test_pmd_mappable(folio)) {
+                       count_vm_event(THP_FILE_FALLBACK);
+                       count_vm_event(THP_FILE_FALLBACK_CHARGE);
+               }
+               goto unacct;
+       }
+
+       error = shmem_add_to_page_cache(folio, mapping, hindex, NULL, gfp);
        if (error)
                goto unacct;
 
@@ -2644,8 +2632,10 @@ int shmem_mfill_atomic_pte(pmd_t *dst_pmd,
        if (unlikely(pgoff >= max_off))
                goto out_release;
 
-       ret = shmem_add_to_page_cache(folio, mapping, pgoff, NULL,
-                                     gfp & GFP_RECLAIM_MASK, dst_vma->vm_mm);
+       ret = mem_cgroup_charge(folio, dst_vma->vm_mm, gfp);
+       if (ret)
+               goto out_release;
+       ret = shmem_add_to_page_cache(folio, mapping, pgoff, NULL, gfp);
        if (ret)
                goto out_release;