Re: [PATCHv3 29/41] ext4: make ext4_mpage_readpages() hugepage-aware

Kirill A. Shutemov
2016-09-16T12:10:34Z

On Thu, Sep 15, 2016 at 02:55:11PM +0300, Kirill A. Shutemov wrote:
> This patch modifies ext4_mpage_readpages() to deal with huge pages.
>
> We read out 2M at once, so we have to alloc (HPAGE_PMD_NR *
> blocks_per_page) sector_t for that. I'm not entirely happy with kmalloc
> in this codepath, but don't see any other option.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

0-DAY reported this:

compiler: powerpc64-linux-gnu-gcc (Debian 5.4.0-6) 5.4.0 20160609
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cro
+ss
chmod +x ~/bin/make.cross
git checkout d8bfe8f327288810a9a099b15f3c89a834d419a4
# save the attached .config to linux build tree
make.cross ARCH=powerpc

All errors (new ones prefixed by >>):

In file included from include/linux/linkage.h:4:0,
from include/linux/kernel.h:6,
from fs/ext4/readpage.c:30:
fs/ext4/readpage.c: In function 'ext4_mpage_readpages':
>> include/linux/compiler.h:491:38: error: call to '__compiletime_assert_144' declared with attribute error:
+BUILD_BUG_ON failed: BIO_MAX_PAGES < HPAGE_PMD_NR
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^
include/linux/compiler.h:474:4: note: in definition of macro '__compiletime_assert'
prefix ## suffix(); \
^
include/linux/compiler.h:491:2: note: in expansion of macro '_compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
^
include/linux/bug.h:51:37: note: in expansion of macro 'compiletime_assert'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
include/linux/bug.h:75:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^
fs/ext4/readpage.c:144:4: note: in expansion of macro 'BUILD_BUG_ON'
BUILD_BUG_ON(BIO_MAX_PAGES < HPAGE_PMD_NR);
^

The fixup:

diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index 6d7cbddceeb2..75b2a7700c9a 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -140,7 +140,8 @@ int ext4_mpage_readpages(struct address_space *mapping,

block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);

- if (PageTransHuge(page)) {
+ if (PageTransHuge(page) &&
+ IS_ENABLED(TRANSPARENT_HUGE_PAGECACHE)) {
BUILD_BUG_ON(BIO_MAX_PAGES < HPAGE_PMD_NR);
nr = HPAGE_PMD_NR * blocks_per_page;
/* XXX: need a better solution ? */
--
Kirill A. Shutemov