From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f69.google.com (mail-it0-f69.google.com [209.85.214.69]) by kanga.kvack.org (Postfix) with ESMTP id 954816B0005 for ; Tue, 24 Apr 2018 07:24:00 -0400 (EDT) Received: by mail-it0-f69.google.com with SMTP id u15-v6so11185346ita.8 for ; Tue, 24 Apr 2018 04:24:00 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id g129-v6sor5191435itd.46.2018.04.24.04.23.59 for (Google Transport Security); Tue, 24 Apr 2018 04:23:59 -0700 (PDT) Date: Tue, 24 Apr 2018 14:23:59 +0300 From: "Kirill A. Shutemov" Subject: Re: [RFC v4 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on Message-ID: <20180424112359.svngcdudzodobvmu@kshutemo-mobl1.Home> References: <1524542450-92577-1-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1524542450-92577-1-git-send-email-yang.shi@linux.alibaba.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi 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 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)) > + stat->blksize = HPAGE_PMD_SIZE; > +#endif > + > return 0; > } > > -- > 1.8.3.1 > -- Kirill A. Shutemov