tmpfs: copy truncate_inode_pages_range

Bring truncate.c's code for truncate_inode_pages_range() inline into
shmem_truncate_range(), replacing its first call (there's a followup
call below, but leave that one, it will disappear next).

Don't play with it yet, apart from leaving out the cleancache flush, and
(importantly) the nrpages == 0 skip, and moving shmem_setattr()'s
partial page preparation into its partial page handling.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 79 insertions, 20 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 24e95ac1605..e101c211ed1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -50,6 +50,7 @@ static struct vfsmount *shm_mnt;
 #include <linux/shmem_fs.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
+#include <linux/pagevec.h>
 #include <linux/percpu_counter.h>
 #include <linux/splice.h>
 #include <linux/security.h>
@@ -242,11 +243,88 @@ 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);
+        struct pagevec pvec;
         pgoff_t index;
         swp_entry_t swap;
+        int i;
+
+        BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
+
+        pagevec_init(&pvec, 0);
+        index = start;
+        while (index <= end && pagevec_lookup(&pvec, mapping, index,
+                        min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
+                mem_cgroup_uncharge_start();
+                for (i = 0; i < pagevec_count(&pvec); i++) {
+                        struct page *page = pvec.pages[i];
+
+                        /* We rely upon deletion not changing page->index */
+                        index = page->index;
+                        if (index > end)
+                                break;
+
+                        if (!trylock_page(page))
+                                continue;
+                        WARN_ON(page->index != index);
+                        if (PageWriteback(page)) {
+                                unlock_page(page);
+                                continue;
+                        }
+                        truncate_inode_page(mapping, page);
+                        unlock_page(page);
+                }
+                pagevec_release(&pvec);
+                mem_cgroup_uncharge_end();
+                cond_resched();
+                index++;
+        }
+
+        if (partial) {
+                struct page *page = NULL;
+                shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
+                if (page) {
+                        zero_user_segment(page, partial, PAGE_CACHE_SIZE);
+                        set_page_dirty(page);
+                        unlock_page(page);
+                        page_cache_release(page);
+                }
+        }
+
+        index = start;
+        for ( ; ; ) {
+                cond_resched();
+                if (!pagevec_lookup(&pvec, mapping, index,
+                        min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
+                        if (index == start)
+                                break;
+                        index = start;
+                        continue;
+                }
+                if (index == start && pvec.pages[0]->index > end) {
+                        pagevec_release(&pvec);
+                        break;
+                }
+                mem_cgroup_uncharge_start();
+                for (i = 0; i < pagevec_count(&pvec); i++) {
+                        struct page *page = pvec.pages[i];
 
-        truncate_inode_pages_range(mapping, lstart, lend);
+                        /* We rely upon deletion not changing page->index */
+                        index = page->index;
+                        if (index > end)
+                                break;
+
+                        lock_page(page);
+                        WARN_ON(page->index != index);
+                        wait_on_page_writeback(page);
+                        truncate_inode_page(mapping, page);
+                        unlock_page(page);
+                }
+                pagevec_release(&pvec);
+                mem_cgroup_uncharge_end();
+                index++;
+        }
 
         if (end > SHMEM_NR_DIRECT)
                 end = SHMEM_NR_DIRECT;
@@ -289,24 +367,7 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
         if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
                 loff_t oldsize = inode->i_size;
                 loff_t newsize = attr->ia_size;
-                struct page *page = NULL;
 
-                if (newsize < oldsize) {
-                        /*
-                         * If truncating down to a partial page, then
-                         * if that page is already allocated, hold it
-                         * in memory until the truncation is over, so
-                         * truncate_partial_page cannot miss it were
-                         * it assigned to swap.
-                         */
-                        if (newsize & (PAGE_CACHE_SIZE-1)) {
-                                (void) shmem_getpage(inode,
-                                        newsize >> PAGE_CACHE_SHIFT,
-                                                &page, SGP_READ, NULL);
-                                if (page)
-                                        unlock_page(page);
-                        }
-                }
                 if (newsize != oldsize) {
                         i_size_write(inode, newsize);
                         inode->i_ctime = inode->i_mtime = CURRENT_TIME;
@@ -318,8 +379,6 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
                         /* unmap again to remove racily COWed private pages */
                         unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
                 }
-                if (page)
-                        page_cache_release(page);
         }
 
         setattr_copy(inode, attr);