[PATCH 05/10] tmpfs: mem_cgroup charge fault to vm_mm not current mm

Hugh Dickins
2016-04-05T20:47:59Z

From: Andres Lagar-Cavilla <andreslc@google.com>

Although shmem_fault() has been careful to count a major fault to vm_mm,
shmem_getpage_gfp() has been careless in charging a remote access fault
to current->mm owner's memcg instead of to vma->vm_mm owner's memcg:
that is inconsistent with all the mem_cgroup charging on remote access
faults in mm/memory.c.

Fix it by passing fault_mm along with fault_type to shmem_get_page_gfp();
but in that case, now knowing the right mm, it's better for it to handle
the PGMAJFAULT updates itself.

And let's keep this clutter out of most callers' way: change the common
shmem_getpage() wrapper to hide fault_mm and fault_type as well as gfp.

Signed-off-by: Andres Lagar-Cavilla <andreslc@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/shmem.c | 61 ++++++++++++++++++++++++++++-----------------------
1 file changed, 34 insertions(+), 27 deletions(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -121,13 +121,14 @@ static bool shmem_should_replace_page(st
static int shmem_replace_page(struct page **pagep, gfp_t gfp,
struct shmem_inode_info *info, pgoff_t index);
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
- struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type);
+ struct page **pagep, enum sgp_type sgp,
+ gfp_t gfp, struct mm_struct *fault_mm, int *fault_type);

static inline int shmem_getpage(struct inode *inode, pgoff_t index,
- struct page **pagep, enum sgp_type sgp, int *fault_type)
+ struct page **pagep, enum sgp_type sgp)
{
return shmem_getpage_gfp(inode, index, pagep, sgp,
- mapping_gfp_mask(inode->i_mapping), fault_type);
+ mapping_gfp_mask(inode->i_mapping), NULL, NULL);
}

static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
@@ -527,7 +528,7 @@ static void shmem_undo_range(struct inod

if (partial_start) {
struct page *page = NULL;
- shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
+ shmem_getpage(inode, start - 1, &page, SGP_READ);
if (page) {
unsigned int top = PAGE_SIZE;
if (start > end) {
@@ -542,7 +543,7 @@ static void shmem_undo_range(struct inod
}
if (partial_end) {
struct page *page = NULL;
- shmem_getpage(inode, end, &page, SGP_READ, NULL);
+ shmem_getpage(inode, end, &page, SGP_READ);
if (page) {
zero_user_segment(page, 0, partial_end);
set_page_dirty(page);
@@ -1115,14 +1116,19 @@ static int shmem_replace_page(struct pag
*
* If we allocate a new one we do not mark it dirty. That's up to the
* vm. If we swap it in we mark it dirty since we also free the swap
- * entry since a page cannot live in both the swap and page cache
+ * entry since a page cannot live in both the swap and page cache.
+ *
+ * fault_mm and fault_type are only supplied by shmem_fault:
+ * otherwise they are NULL.
*/
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
- struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type)
+ struct page **pagep, enum sgp_type sgp, gfp_t gfp,
+ struct mm_struct *fault_mm, int *fault_type)
{
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info;
struct shmem_sb_info *sbinfo;
+ struct mm_struct *charge_mm;
struct mem_cgroup *memcg;
struct page *page;
swp_entry_t swap;
@@ -1168,14 +1174,19 @@ repeat:
*/
info = SHMEM_I(inode);
sbinfo = SHMEM_SB(inode->i_sb);
+ charge_mm = fault_mm ? : current->mm;

if (swap.val) {
/* Look it up and read it in.. */
page = lookup_swap_cache(swap);
if (!page) {
- /* here we actually do the io */
- if (fault_type)
+ /* Or update major stats only when swapin succeeds?? */
+ if (fault_type) {
*fault_type |= VM_FAULT_MAJOR;
+ count_vm_event(PGMAJFAULT);
+ mem_cgroup_count_vm_event(fault_mm, PGMAJFAULT);
+ }
+ /* Here we actually start the io */
page = shmem_swapin(swap, gfp, info, index);
if (!page) {
error = -ENOMEM;
@@ -1202,7 +1213,7 @@ repeat:
goto failed;
}

- error = mem_cgroup_try_charge(page, current->mm, gfp, &memcg,
+ error = mem_cgroup_try_charge(page, charge_mm, gfp, &memcg,
false);
if (!error) {
error = shmem_add_to_page_cache(page, mapping, index,
@@ -1263,7 +1274,7 @@ repeat:
if (sgp == SGP_WRITE)
__SetPageReferenced(page);

- error = mem_cgroup_try_charge(page, current->mm, gfp, &memcg,
+ error = mem_cgroup_try_charge(page, charge_mm, gfp, &memcg,
false);
if (error)
goto decused;
@@ -1352,6 +1363,7 @@ unlock:
static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
struct inode *inode = file_inode(vma->vm_file);
+ gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
int error;
int ret = VM_FAULT_LOCKED;

@@ -1413,14 +1425,10 @@ static int shmem_fault(struct vm_area_st
spin_unlock(&inode->i_lock);
}

- error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
+ error = shmem_getpage_gfp(inode, vmf->pgoff, &vmf->page, SGP_CACHE,
+ gfp, vma->vm_mm, &ret);
if (error)
return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
-
- if (ret & VM_FAULT_MAJOR) {
- count_vm_event(PGMAJFAULT);
- mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
- }
return ret;
}

@@ -1567,7 +1575,7 @@ shmem_write_begin(struct file *file, str
return -EPERM;
}

- return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
+ return shmem_getpage(inode, index, pagep, SGP_WRITE);
}

static int
@@ -1633,7 +1641,7 @@ static ssize_t shmem_file_read_iter(stru
break;
}

- error = shmem_getpage(inode, index, &page, sgp, NULL);
+ error = shmem_getpage(inode, index, &page, sgp);
if (error) {
if (error == -EINVAL)
error = 0;
@@ -1749,7 +1757,7 @@ static ssize_t shmem_file_splice_read(st
error = 0;

while (spd.nr_pages < nr_pages) {
- error = shmem_getpage(inode, index, &page, SGP_CACHE, NULL);
+ error = shmem_getpage(inode, index, &page, SGP_CACHE);
if (error)
break;
unlock_page(page);
@@ -1771,8 +1779,7 @@ static ssize_t shmem_file_splice_read(st
page = spd.pages[page_nr];

if (!PageUptodate(page) || page->mapping != mapping) {
- error = shmem_getpage(inode, index, &page,
- SGP_CACHE, NULL);
+ error = shmem_getpage(inode, index, &page, SGP_CACHE);
if (error)
break;
unlock_page(page);
@@ -2215,8 +2222,7 @@ static long shmem_fallocate(struct file
else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
error = -ENOMEM;
else
- error = shmem_getpage(inode, index, &page, SGP_FALLOC,
- NULL);
+ error = shmem_getpage(inode, index, &page, SGP_FALLOC);
if (error) {
/* Remove the !PageUptodate pages we added */
shmem_undo_range(inode,
@@ -2534,7 +2540,7 @@ static int shmem_symlink(struct inode *d
inode->i_op = &shmem_short_symlink_operations;
} else {
inode_nohighmem(inode);
- error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
+ error = shmem_getpage(inode, 0, &page, SGP_WRITE);
if (error) {
iput(inode);
return error;
@@ -2575,7 +2581,7 @@ static const char *shmem_get_link(struct
return ERR_PTR(-ECHILD);
}
} else {
- error = shmem_getpage(inode, 0, &page, SGP_READ, NULL);
+ error = shmem_getpage(inode, 0, &page, SGP_READ);
if (error)
return ERR_PTR(error);
unlock_page(page);
@@ -3478,7 +3484,8 @@ struct page *shmem_read_mapping_page_gfp
int error;

BUG_ON(mapping->a_ops != &shmem_aops);
- error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE, gfp, NULL);
+ error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE,
+ gfp, NULL, NULL);
if (error)
page = ERR_PTR(error);
else