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-rw-r--r--mm/shmem.c58
1 files changed, 56 insertions, 2 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 793dcd1..191663a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -84,6 +84,18 @@ struct shmem_xattr {
char value[0];
};
+/*
+ * shmem_fallocate and shmem_writepage communicate via inode->i_private
+ * (with i_mutex making sure that it has only one user at a time):
+ * we would prefer not to enlarge the shmem inode just for that.
+ */
+struct shmem_falloc {
+ pgoff_t start; /* start of range currently being fallocated */
+ pgoff_t next; /* the next page offset to be fallocated */
+ pgoff_t nr_falloced; /* how many new pages have been fallocated */
+ pgoff_t nr_unswapped; /* how often writepage refused to swap out */
+};
+
/* Flag allocation requirements to shmem_getpage */
enum sgp_type {
SGP_READ, /* don't exceed i_size, don't allocate page */
@@ -791,8 +803,28 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
* This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
* value into swapfile.c, the only way we can correctly account for a
* fallocated page arriving here is now to initialize it and write it.
+ *
+ * That's okay for a page already fallocated earlier, but if we have
+ * not yet completed the fallocation, then (a) we want to keep track
+ * of this page in case we have to undo it, and (b) it may not be a
+ * good idea to continue anyway, once we're pushing into swap. So
+ * reactivate the page, and let shmem_fallocate() quit when too many.
*/
if (!PageUptodate(page)) {
+ if (inode->i_private) {
+ struct shmem_falloc *shmem_falloc;
+ spin_lock(&inode->i_lock);
+ shmem_falloc = inode->i_private;
+ if (shmem_falloc &&
+ index >= shmem_falloc->start &&
+ index < shmem_falloc->next)
+ shmem_falloc->nr_unswapped++;
+ else
+ shmem_falloc = NULL;
+ spin_unlock(&inode->i_lock);
+ if (shmem_falloc)
+ goto redirty;
+ }
clear_highpage(page);
flush_dcache_page(page);
SetPageUptodate(page);
@@ -1647,6 +1679,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
{
struct inode *inode = file->f_path.dentry->d_inode;
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+ struct shmem_falloc shmem_falloc;
pgoff_t start, index, end;
int error;
@@ -1679,6 +1712,14 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
goto out;
}
+ shmem_falloc.start = start;
+ shmem_falloc.next = start;
+ shmem_falloc.nr_falloced = 0;
+ shmem_falloc.nr_unswapped = 0;
+ spin_lock(&inode->i_lock);
+ inode->i_private = &shmem_falloc;
+ spin_unlock(&inode->i_lock);
+
for (index = start; index < end; index++) {
struct page *page;
@@ -1688,6 +1729,8 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
*/
if (signal_pending(current))
error = -EINTR;
+ else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
+ error = -ENOMEM;
else
error = shmem_getpage(inode, index, &page, SGP_FALLOC,
NULL);
@@ -1696,10 +1739,18 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
shmem_undo_range(inode,
(loff_t)start << PAGE_CACHE_SHIFT,
(loff_t)index << PAGE_CACHE_SHIFT, true);
- goto ctime;
+ goto undone;
}
/*
+ * Inform shmem_writepage() how far we have reached.
+ * No need for lock or barrier: we have the page lock.
+ */
+ shmem_falloc.next++;
+ if (!PageUptodate(page))
+ shmem_falloc.nr_falloced++;
+
+ /*
* If !PageUptodate, leave it that way so that freeable pages
* can be recognized if we need to rollback on error later.
* But set_page_dirty so that memory pressure will swap rather
@@ -1714,8 +1765,11 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
i_size_write(inode, offset + len);
-ctime:
inode->i_ctime = CURRENT_TIME;
+undone:
+ spin_lock(&inode->i_lock);
+ inode->i_private = NULL;
+ spin_unlock(&inode->i_lock);
out:
mutex_unlock(&inode->i_mutex);
return error;
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