[PATCH] shmem_populate: avoid an useless check, and some comments

Either shmem_getpage returns a failure, or it found a page, or it was told
it couldn't do any I/O.  So it's useless to check nonblock in the else
branch.  We could add a BUG() there but I preferred to comment the
offending function.

This was taken out from one Ingo Molnar's old patch I'm resurrecting.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index edc5443..8861192 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1504,8 +1504,12 @@ repeat:
                return -EINVAL;
 
        page = filemap_getpage(file, pgoff, nonblock);
+
+       /* XXX: This is wrong, a filesystem I/O error may have happened. Fix that as
+        * done in shmem_populate calling shmem_getpage */
        if (!page && !nonblock)
                return -ENOMEM;
+
        if (page) {
                err = install_page(mm, vma, addr, page, prot);
                if (err) {
@@ -1513,6 +1517,9 @@ repeat:
                        return err;
                }
        } else {
+               /* No page was found just because we can't read it in now (being
+                * here implies nonblock != 0), but the page may exist, so set
+                * the PTE to fault it in later. */
                err = install_file_pte(mm, vma, addr, pgoff, prot);
                if (err)
                        return err;

diff --git a/mm/shmem.c b/mm/shmem.c
index 5a81b1e..08a3bc2 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1195,6 +1195,7 @@ static int shmem_populate(struct vm_area_struct *vma,
                err = shmem_getpage(inode, pgoff, &page, sgp, NULL);
                if (err)
                        return err;
+               /* Page may still be null, but only if nonblock was set. */
                if (page) {
                        mark_page_accessed(page);
                        err = install_page(mm, vma, addr, page, prot);
@@ -1202,7 +1203,10 @@ static int shmem_populate(struct vm_area_struct *vma,
                                page_cache_release(page);
                                return err;
                        }
-               } else if (nonblock) {
+               } else {
+                       /* No page was found just because we can't read it in
+                        * now (being here implies nonblock != 0), but the page
+                        * may exist, so set the PTE to fault it in later. */
                        err = install_file_pte(mm, vma, addr, pgoff, prot);
                        if (err)
                                return err;