From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f170.google.com (mail-pd0-f170.google.com [209.85.192.170]) by kanga.kvack.org (Postfix) with ESMTP id 52C726B0255 for ; Mon, 17 Aug 2015 19:44:36 -0400 (EDT) Received: by pdrh1 with SMTP id h1so61508511pdr.0 for ; Mon, 17 Aug 2015 16:44:35 -0700 (PDT) Received: from mail-pd0-x22c.google.com (mail-pd0-x22c.google.com. [2607:f8b0:400e:c02::22c]) by mx.google.com with ESMTPS id zc8si26972922pac.59.2015.08.17.16.44.35 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 17 Aug 2015 16:44:35 -0700 (PDT) Received: by pdob1 with SMTP id b1so5426121pdo.2 for ; Mon, 17 Aug 2015 16:44:35 -0700 (PDT) Date: Mon, 17 Aug 2015 16:43:13 -0700 (PDT) From: Hugh Dickins Subject: Re: [PATCH] shmem: recalculate file inode when fstat In-Reply-To: <1436558977-31712-1-git-send-email-yuzhao@google.com> Message-ID: References: <1436558977-31712-1-git-send-email-yuzhao@google.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Yu Zhao Cc: Andrew Morton , Hugh Dickins , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri, 10 Jul 2015, Yu Zhao wrote: > Shmem uses shmem_recalc_inode to update i_blocks when it allocates > page, undoes range or swaps. But mm can drop clean page without > notifying shmem. This makes fstat sometimes return out-of-date > block size. > > The problem can be partially solved when we add > inode_operations->getattr which calls shmem_recalc_inode to update > i_blocks for fstat. > > shmem_recalc_inode also updates counter used by statfs and > vm_committed_as. For them the situation is not changed. They still > suffer from the discrepancy after dropping clean page and before > the function is called by aforementioned triggers. "partially" indeed. Thanks, your patch is sensible in itself, though nobody cared before; and I hope nobody is fooled by your improvement into thinking that shmem_recalc_inode() does a very good job. I looked once again into how to improve the situation, but yet again had to retreat for now: as I found before, mapping->a_ops->freepage almost does what's needed, but is frustratingly not quite usable. So let's go with your patch: I'll add my signoff and send on to akpm for 4.3. Hugh > > Signed-off-by: Yu Zhao > --- > mm/shmem.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 4caf8ed..37e7933 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -542,6 +542,21 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend) > } > EXPORT_SYMBOL_GPL(shmem_truncate_range); > > +static int shmem_getattr(struct vfsmount *mnt, struct dentry *dentry, > + struct kstat *stat) > +{ > + struct inode *inode = dentry->d_inode; > + struct shmem_inode_info *info = SHMEM_I(inode); > + > + spin_lock(&info->lock); > + shmem_recalc_inode(inode); > + spin_unlock(&info->lock); > + > + generic_fillattr(inode, stat); > + > + return 0; > +} > + > static int shmem_setattr(struct dentry *dentry, struct iattr *attr) > { > struct inode *inode = d_inode(dentry); > @@ -3122,6 +3137,7 @@ static const struct file_operations shmem_file_operations = { > }; > > static const struct inode_operations shmem_inode_operations = { > + .getattr = shmem_getattr, > .setattr = shmem_setattr, > #ifdef CONFIG_TMPFS_XATTR > .setxattr = shmem_setxattr, > -- > 2.4.3.573.g4eafbef -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org