[patch 02/39] shmem_populate: avoid an useless check, and some comments

[blaisorblade@yahoo.it]

From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

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.

References: commit b103e8b204b317d52834671d5f09db95645523c2 of old-2.6-bkcvs,
pointing to BKrev: 3f5ed0c1llm6NnNwNXtPv-Z0IYzkwA

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

 linux-2.6.git-paolo/mm/filemap.c |    7 +++++++
 linux-2.6.git-paolo/mm/shmem.c   |    6 +++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff -puN mm/shmem.c~mm-populate-optim-comment mm/shmem.c
--- linux-2.6.git/mm/shmem.c~mm-populate-optim-comment	2005-08-11 11:12:39.000000000 +0200
+++ linux-2.6.git-paolo/mm/shmem.c	2005-08-11 11:12:39.000000000 +0200
@@ -1195,6 +1195,7 @@ static int shmem_populate(struct vm_area
 		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
 				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;
diff -puN mm/filemap.c~mm-populate-optim-comment mm/filemap.c
--- linux-2.6.git/mm/filemap.c~mm-populate-optim-comment	2005-08-11 11:12:39.000000000 +0200
+++ linux-2.6.git-paolo/mm/filemap.c	2005-08-11 11:12:39.000000000 +0200
@@ -1505,8 +1505,12 @@ 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) {
@@ -1514,6 +1518,9 @@ 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;
_
-
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