From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Yang Shi To: kirill.shutemov@linux.intel.com, hughd@google.com, mhocko@kernel.org, hch@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org Cc: yang.shi@linux.alibaba.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [RFC v4 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on Date: Tue, 24 Apr 2018 12:00:50 +0800 Message-Id: <1524542450-92577-1-git-send-email-yang.shi@linux.alibaba.com> Sender: owner-linux-mm@kvack.org List-ID: Since tmpfs THP was supported in 4.8, hugetlbfs is not the only filesystem with huge page support anymore. tmpfs can use huge page via THP when mounting by "huge=" mount option. When applications use huge page on hugetlbfs, it just need check the filesystem magic number, but it is not enough for tmpfs. Make stat.st_blksize return huge page size if it is mounted by appropriate "huge=" option to give applications a hint to optimize the behavior with THP. Some applications may not do wisely with THP. For example, QEMU may mmap file on non huge page aligned hint address with MAP_FIXED, which results in no pages are PMD mapped even though THP is used. Some applications may mmap file with non huge page aligned offset. Both behaviors make THP pointless. statfs.f_bsize still returns 4KB for tmpfs since THP could be split, and it also may fallback to 4KB page silently if there is not enough huge page. Furthermore, different f_bsize makes max_blocks and free_blocks calculation harder but without too much benefit. Returning huge page size via stat.st_blksize sounds good enough. Since PUD size huge page for THP has not been supported, now it just returns HPAGE_PMD_SIZE. Signed-off-by: Yang Shi Cc: "Kirill A. Shutemov" Cc: Hugh Dickins Cc: Michal Hocko Cc: Alexander Viro Suggested-by: Christoph Hellwig --- v3 --> v4: * Rework the commit log per the education from Michal and Kirill * Fix build error if CONFIG_TRANSPARENT_HUGEPAGE is disabled v2 --> v3: * Use shmem_sb_info.huge instead of global variable per Michal's comment v2 --> v1: * Adopted the suggestion from hch to return huge page size via st_blksize instead of creating a new flag. mm/shmem.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index b859192..19b8055 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -988,6 +988,7 @@ static int shmem_getattr(const struct path *path, struct kstat *stat, { struct inode *inode = path->dentry->d_inode; struct shmem_inode_info *info = SHMEM_I(inode); + struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb); if (info->alloced - info->swapped != inode->i_mapping->nrpages) { spin_lock_irq(&info->lock); @@ -995,6 +996,11 @@ static int shmem_getattr(const struct path *path, struct kstat *stat, spin_unlock_irq(&info->lock); } generic_fillattr(inode, stat); +#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE + if (sbinfo->huge > 0) + stat->blksize = HPAGE_PMD_SIZE; +#endif + return 0; } -- 1.8.3.1