From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [RFC v4 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on To: "Kirill A. Shutemov" Cc: kirill.shutemov@linux.intel.com, hughd@google.com, mhocko@kernel.org, hch@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1524542450-92577-1-git-send-email-yang.shi@linux.alibaba.com> <20180424112359.svngcdudzodobvmu@kshutemo-mobl1.Home> From: Yang Shi Message-ID: <9cd455b9-ae84-8ea9-b3a0-488fe709d1bd@linux.alibaba.com> Date: Tue, 24 Apr 2018 07:07:59 -0600 MIME-Version: 1.0 In-Reply-To: <20180424112359.svngcdudzodobvmu@kshutemo-mobl1.Home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: On 4/24/18 5:23 AM, Kirill A. Shutemov wrote: > On Tue, Apr 24, 2018 at 12:00:50PM +0800, Yang Shi wrote: >> 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) > No ifdeffery, please. > > And we probably want to check if shmem_huge is 'force'. > > Something like this? > > if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) && > (shmem_huge == SHMEM_HUGE_FORCE || sbinfo->huge)) Yes, looks good, will do that. I missed "force" part, just realized it is applicable to all mounts. Thanks, Yang > >> + stat->blksize = HPAGE_PMD_SIZE; >> +#endif >> + >> return 0; >> } >> >> -- >> 1.8.3.1 >>