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

[Kirill A. Shutemov]

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@xxxxxxxxxxxxxxx>

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