@@ -2736,7 +2736,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
inode->i_private = &shmem_falloc;
spin_unlock(&inode->i_lock);
- for (index = start; index < end; index++) {
+ for (index = start; index < end; ) {
struct page *page;
/*
@@ -2759,13 +2759,26 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
goto undone;
}
+ index++;
+ /*
+ * Here is a more important optimization than it appears:
+ * a second SGP_FALLOC on the same huge page will clear it,
+ * making it PageUptodate and un-undoable if we fail later.
+ */
+ if (PageTransCompound(page)) {
+ index = round_up(index, HPAGE_PMD_NR);
+ /* Beware 32-bit wraparound */
+ if (!index)
+ index--;
+ }
+
/*
* 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++;
+ shmem_falloc.nr_falloced += index - shmem_falloc.next;
+ shmem_falloc.next = index;
/*
* If !PageUptodate, leave it that way so that freeable pages
shmem_fallocate() goes to a lot of trouble to leave its newly allocated pages !Uptodate, partly to identify and undo them on failure, partly to leave the overhead of clearing them until later. But the huge page case did not skip to the end of the extent, walked through the tail pages one by one, and appeared to work just fine: but in doing so, cleared and Uptodated the huge page, so there was no way to undo it on failure. And by setting Uptodate too soon, it messed up both its nr_falloced and nr_unswapped counts, so that the intended "time to give up" heuristic did not work at all. Now advance immediately to the end of the huge extent, with a comment on why this is more than just an optimization. But although this speeds up huge tmpfs fallocation, it does leave the clearing until first use, and some users may have come to appreciate slow fallocate but fast first use: if they complain, then we can consider adding a pass to clear at the end. Fixes: 800d8c63b2e9 ("shmem: add huge pages support") Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Yang Shi <shy828301@gmail.com> --- mm/shmem.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-)