[PATCH 1/4] tmpfs: support fallocate FALLOC_FL_PUNCH_HOLE

From: John Stultz
Date: Fri May 25 2012 - 15:18:57 EST


From: Hugh Dickins <hughd@xxxxxxxxxx>

tmpfs has supported hole-punching since 2.6.16, via madvise(,,MADV_REMOVE).
But nowadays fallocate(,FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE,,) is the
agreed way to punch holes.

So add shmem_fallocate() to support that, and tweak shmem_truncate_range()
to support partial pages at both the beginning and end of range (never
needed for madvise, which demands rounded addr and rounds up length).

CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Android Kernel Team <kernel-team@xxxxxxxxxxx>
CC: Robert Love <rlove@xxxxxxxxxx>
CC: Mel Gorman <mel@xxxxxxxxx>
CC: Hugh Dickins <hughd@xxxxxxxxxx>
CC: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>
CC: Rik van Riel <riel@xxxxxxxxxx>
CC: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>
CC: Dave Chinner <david@xxxxxxxxxxxxx>
CC: Neil Brown <neilb@xxxxxxx>
CC: Andrea Righi <andrea@xxxxxxxxxxxxxxx>
CC: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
CC: Taras Glek <tgek@xxxxxxxxxxx>
CC: Mike Hommey <mh@xxxxxxxxxxxx>

Based-on-patch-by: Cong Wang <amwang@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
mm/shmem.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
1 files changed, 57 insertions(+), 11 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index d7b433a..9b1c6b4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -53,6 +53,7 @@ static struct vfsmount *shm_mnt;
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/percpu_counter.h>
+#include <linux/falloc.h>
#include <linux/splice.h>
#include <linux/security.h>
#include <linux/swapops.h>
@@ -429,21 +430,23 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info = SHMEM_I(inode);
pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
- unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);
- pgoff_t end = (lend >> PAGE_CACHE_SHIFT);
+ pgoff_t end = (lend + 1) >> PAGE_CACHE_SHIFT;
+ unsigned int partial_start = lstart & (PAGE_CACHE_SIZE - 1);
+ unsigned int partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1);
struct pagevec pvec;
pgoff_t indices[PAGEVEC_SIZE];
long nr_swaps_freed = 0;
pgoff_t index;
int i;

- BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
+ if (lend == -1)
+ end = -1; /* unsigned, so actually very big */

pagevec_init(&pvec, 0);
index = start;
- while (index <= end) {
+ while (index < end) {
pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
- min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
+ min(end - index, (pgoff_t)PAGEVEC_SIZE),
pvec.pages, indices);
if (!pvec.nr)
break;
@@ -452,7 +455,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
struct page *page = pvec.pages[i];

index = indices[i];
- if (index > end)
+ if (index >= end)
break;

if (radix_tree_exceptional_entry(page)) {
@@ -476,22 +479,39 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
index++;
}

- if (partial) {
+ if (partial_start) {
struct page *page = NULL;
shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
if (page) {
- zero_user_segment(page, partial, PAGE_CACHE_SIZE);
+ unsigned int top = PAGE_CACHE_SIZE;
+ if (start > end) {
+ top = partial_end;
+ partial_end = 0;
+ }
+ zero_user_segment(page, partial_start, top);
+ set_page_dirty(page);
+ unlock_page(page);
+ page_cache_release(page);
+ }
+ }
+ if (partial_end) {
+ struct page *page = NULL;
+ shmem_getpage(inode, end, &page, SGP_READ, NULL);
+ if (page) {
+ zero_user_segment(page, 0, partial_end);
set_page_dirty(page);
unlock_page(page);
page_cache_release(page);
}
}
+ if (start >= end)
+ return;

index = start;
for ( ; ; ) {
cond_resched();
pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
- min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
+ min(end - index, (pgoff_t)PAGEVEC_SIZE),
pvec.pages, indices);
if (!pvec.nr) {
if (index == start)
@@ -499,7 +519,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
index = start;
continue;
}
- if (index == start && indices[0] > end) {
+ if (index == start && indices[0] >= end) {
shmem_deswap_pagevec(&pvec);
pagevec_release(&pvec);
break;
@@ -509,7 +529,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
struct page *page = pvec.pages[i];

index = indices[i];
- if (index > end)
+ if (index >= end)
break;

if (radix_tree_exceptional_entry(page)) {
@@ -1462,6 +1482,31 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
return error;
}

+static long shmem_fallocate(struct file *file, int mode, loff_t offset,
+ loff_t len)
+{
+ struct inode *inode = file->f_path.dentry->d_inode;
+ int error = -EOPNOTSUPP;
+
+ mutex_lock(&inode->i_mutex);
+
+ if (mode & FALLOC_FL_PUNCH_HOLE) {
+ struct address_space *mapping = file->f_mapping;
+ loff_t unmap_start = round_up(offset, PAGE_SIZE);
+ loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
+
+ if ((u64)unmap_end > (u64)unmap_start)
+ unmap_mapping_range(mapping, unmap_start,
+ 1 + unmap_end - unmap_start, 0);
+ shmem_truncate_range(inode, offset, offset + len - 1);
+ /* No need to unmap again: hole-punching leaves COWed pages */
+ error = 0;
+ }
+
+ mutex_unlock(&inode->i_mutex);
+ return error;
+}
+
static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);
@@ -2372,6 +2417,7 @@ static const struct file_operations shmem_file_operations = {
.fsync = noop_fsync,
.splice_read = shmem_file_splice_read,
.splice_write = generic_file_splice_write,
+ .fallocate = shmem_fallocate,
#endif
};

--
1.7.3.2.146.gca209

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