Skip to content

Commit

Permalink
shmem: split huge pages beyond i_size under memory pressure
Browse files Browse the repository at this point in the history 
Even if user asked to allocate huge pages always (huge=always), we
should be able to free up some memory by splitting pages which are
partly byound i_size if memory presure comes or once we hit limit on
filesystem size (-o size=).

In order to do this we maintain per-superblock list of inodes, which
potentially have huge pages on the border of file size.

Per-fs shrinker can reclaim memory by splitting such pages.

If we hit -ENOSPC during shmem_getpage_gfp(), we try to split a page to
free up space on the filesystem and retry allocation if it succeed.

Link: http://lkml.kernel.org/r/1466021202-61880-37-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
  • Loading branch information
@kiryl @torvalds
kiryl authored and torvalds committed Jul 26, 2016
1 parent e496cf3 commit 779750d
Show file tree
Hide file tree
Showing 2 changed files with 180 additions and 1 deletion.
6 changes: 5 additions & 1 deletion include/linux/shmem_fs.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,9 @@ struct shmem_inode_info {
unsigned long flags;
unsigned long alloced; /* data pages alloced to file */
unsigned long swapped; /* subtotal assigned to swap */
struct shared_policy policy; /* NUMA memory alloc policy */
struct list_head shrinklist; /* shrinkable hpage inodes */
struct list_head swaplist; /* chain of maybes on swap */
struct shared_policy policy; /* NUMA memory alloc policy */
struct simple_xattrs xattrs; /* list of xattrs */
struct inode vfs_inode;
};
Expand All @@ -33,6 +34,9 @@ struct shmem_sb_info {
kuid_t uid; /* Mount uid for root directory */
kgid_t gid; /* Mount gid for root directory */
struct mempolicy *mpol; /* default memory policy for mappings */
spinlock_t shrinklist_lock; /* Protects shrinklist */
struct list_head shrinklist; /* List of shinkable inodes */
unsigned long shrinklist_len; /* Length of shrinklist */
};

static inline struct shmem_inode_info *SHMEM_I(struct inode *inode)
Expand Down
175 changes: 175 additions & 0 deletions mm/shmem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,7 @@ static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
static const struct vm_operations_struct shmem_vm_ops;
static struct file_system_type shmem_fs_type;

static LIST_HEAD(shmem_swaplist);
static DEFINE_MUTEX(shmem_swaplist_mutex);
Expand Down Expand Up @@ -406,10 +407,122 @@ static const char *shmem_format_huge(int huge)
}
}

static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
struct shrink_control *sc, unsigned long nr_to_split)
{
LIST_HEAD(list), *pos, *next;
struct inode *inode;
struct shmem_inode_info *info;
struct page *page;
unsigned long batch = sc ? sc->nr_to_scan : 128;
int removed = 0, split = 0;

if (list_empty(&sbinfo->shrinklist))
return SHRINK_STOP;

spin_lock(&sbinfo->shrinklist_lock);
list_for_each_safe(pos, next, &sbinfo->shrinklist) {
info = list_entry(pos, struct shmem_inode_info, shrinklist);

/* pin the inode */
inode = igrab(&info->vfs_inode);

/* inode is about to be evicted */
if (!inode) {
list_del_init(&info->shrinklist);
removed++;
goto next;
}

/* Check if there's anything to gain */
if (round_up(inode->i_size, PAGE_SIZE) ==
round_up(inode->i_size, HPAGE_PMD_SIZE)) {
list_del_init(&info->shrinklist);
removed++;
iput(inode);
goto next;
}

list_move(&info->shrinklist, &list);
next:
if (!--batch)
break;
}
spin_unlock(&sbinfo->shrinklist_lock);

list_for_each_safe(pos, next, &list) {
int ret;

info = list_entry(pos, struct shmem_inode_info, shrinklist);
inode = &info->vfs_inode;

if (nr_to_split && split >= nr_to_split) {
iput(inode);
continue;
}

page = find_lock_page(inode->i_mapping,
(inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT);
if (!page)
goto drop;

if (!PageTransHuge(page)) {
unlock_page(page);
put_page(page);
goto drop;
}

ret = split_huge_page(page);
unlock_page(page);
put_page(page);

if (ret) {
/* split failed: leave it on the list */
iput(inode);
continue;
}

split++;
drop:
list_del_init(&info->shrinklist);
removed++;
iput(inode);
}

spin_lock(&sbinfo->shrinklist_lock);
list_splice_tail(&list, &sbinfo->shrinklist);
sbinfo->shrinklist_len -= removed;
spin_unlock(&sbinfo->shrinklist_lock);

return split;
}

static long shmem_unused_huge_scan(struct super_block *sb,
struct shrink_control *sc)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

if (!READ_ONCE(sbinfo->shrinklist_len))
return SHRINK_STOP;

return shmem_unused_huge_shrink(sbinfo, sc, 0);
}

static long shmem_unused_huge_count(struct super_block *sb,
struct shrink_control *sc)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
return READ_ONCE(sbinfo->shrinklist_len);
}
#else /* !CONFIG_TRANSPARENT_HUGE_PAGECACHE */

#define shmem_huge SHMEM_HUGE_DENY

static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
struct shrink_control *sc, unsigned long nr_to_split)
{
return 0;
}
#endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE */

/*
Expand Down Expand Up @@ -843,6 +956,7 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
{
struct inode *inode = d_inode(dentry);
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
int error;

error = inode_change_ok(inode, attr);
Expand Down Expand Up @@ -878,6 +992,20 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
if (oldsize > holebegin)
unmap_mapping_range(inode->i_mapping,
holebegin, 0, 1);

/*
* Part of the huge page can be beyond i_size: subject
* to shrink under memory pressure.
*/
if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) {
spin_lock(&sbinfo->shrinklist_lock);
if (list_empty(&info->shrinklist)) {
list_add_tail(&info->shrinklist,
&sbinfo->shrinklist);
sbinfo->shrinklist_len++;
}
spin_unlock(&sbinfo->shrinklist_lock);
}
}
}

Expand All @@ -890,11 +1018,20 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
static void shmem_evict_inode(struct inode *inode)
{
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);

if (inode->i_mapping->a_ops == &shmem_aops) {
shmem_unacct_size(info->flags, inode->i_size);
inode->i_size = 0;
shmem_truncate_range(inode, 0, (loff_t)-1);
if (!list_empty(&info->shrinklist)) {
spin_lock(&sbinfo->shrinklist_lock);
if (!list_empty(&info->shrinklist)) {
list_del_init(&info->shrinklist);
sbinfo->shrinklist_len--;
}
spin_unlock(&sbinfo->shrinklist_lock);
}
if (!list_empty(&info->swaplist)) {
mutex_lock(&shmem_swaplist_mutex);
list_del_init(&info->swaplist);
Expand Down Expand Up @@ -1563,8 +1700,23 @@ alloc_nohuge: page = shmem_alloc_and_acct_page(gfp, info, sbinfo,
index, false);
}
if (IS_ERR(page)) {
int retry = 5;
error = PTR_ERR(page);
page = NULL;
if (error != -ENOSPC)
goto failed;
/*
* Try to reclaim some spece by splitting a huge page
* beyond i_size on the filesystem.
*/
while (retry--) {
int ret;
ret = shmem_unused_huge_shrink(sbinfo, NULL, 1);
if (ret == SHRINK_STOP)
break;
if (ret)
goto alloc_nohuge;
}
goto failed;
}

Expand Down Expand Up @@ -1603,6 +1755,22 @@ alloc_nohuge: page = shmem_alloc_and_acct_page(gfp, info, sbinfo,
spin_unlock_irq(&info->lock);
alloced = true;

if (PageTransHuge(page) &&
DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) <
hindex + HPAGE_PMD_NR - 1) {
/*
* Part of the huge page is beyond i_size: subject
* to shrink under memory pressure.
*/
spin_lock(&sbinfo->shrinklist_lock);
if (list_empty(&info->shrinklist)) {
list_add_tail(&info->shrinklist,
&sbinfo->shrinklist);
sbinfo->shrinklist_len++;
}
spin_unlock(&sbinfo->shrinklist_lock);
}

/*
* Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
*/
Expand Down Expand Up @@ -1920,6 +2088,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
spin_lock_init(&info->lock);
info->seals = F_SEAL_SEAL;
info->flags = flags & VM_NORESERVE;
INIT_LIST_HEAD(&info->shrinklist);
INIT_LIST_HEAD(&info->swaplist);
simple_xattrs_init(&info->xattrs);
cache_no_acl(inode);
Expand Down Expand Up @@ -3518,6 +3687,8 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
if (percpu_counter_init(&sbinfo->used_blocks, 0, GFP_KERNEL))
goto failed;
sbinfo->free_inodes = sbinfo->max_inodes;
spin_lock_init(&sbinfo->shrinklist_lock);
INIT_LIST_HEAD(&sbinfo->shrinklist);

sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_blocksize = PAGE_SIZE;
Expand Down Expand Up @@ -3680,6 +3851,10 @@ static const struct super_operations shmem_ops = {
.evict_inode = shmem_evict_inode,
.drop_inode = generic_delete_inode,
.put_super = shmem_put_super,
#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
.nr_cached_objects = shmem_unused_huge_count,
.free_cached_objects = shmem_unused_huge_scan,
#endif
};

static const struct vm_operations_struct shmem_vm_ops = {
Expand Down

0 comments on commit 779750d

Please sign in to comment.