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From: Chengguang Xu <cgxu519@mykernel.net>
To: "Amir Goldstein" <amir73il@gmail.com>
Cc: "miklos" <miklos@szeredi.hu>, "jack" <jack@suse.cz>,
	"linux-unionfs" <linux-unionfs@vger.kernel.org>,
	"linux-fsdevel" <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH v3 06/10] ovl: mark overlayfs' inode dirty on shared mmap
Date: Thu, 12 Nov 2020 00:09:03 +0800
Message-ID: <175b8114d9a.d35f90865969.6295508804432147693@mykernel.net> (raw)
In-Reply-To: <CAOQ4uxhG__saz3qWpDUzXUNkBuueAAMzBoXXXOnmnAL2JMSKjQ@mail.gmail.com>

 ---- 在 星期三, 2020-11-11 23:20:56 Amir Goldstein <amir73il@gmail.com> 撰写 ----
 > On Wed, Nov 11, 2020 at 3:05 PM Chengguang Xu <cgxu519@mykernel.net> wrote:
 > >
 > >  ---- 在 星期日, 2020-11-08 22:03:03 Chengguang Xu <cgxu519@mykernel.net> 撰写 ----
 > >  > Overlayfs cannot be notified when mmapped area gets dirty,
 > >  > so we need to proactively mark inode dirty in ->mmap operation.
 > >  >
 > >  > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
 > >  > ---
 > >  >  fs/overlayfs/file.c | 2 ++
 > >  >  1 file changed, 2 insertions(+)
 > >  >
 > >  > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
 > >  > index efccb7c1f9bc..662252047fff 100644
 > >  > --- a/fs/overlayfs/file.c
 > >  > +++ b/fs/overlayfs/file.c
 > >  > @@ -486,6 +486,8 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 > >  >          /* Drop reference count from new vm_file value */
 > >  >          fput(realfile);
 > >  >      } else {
 > >  > +        if (vma->vm_flags & (VM_SHARED|VM_MAYSHARE))
 > >
 > > Maybe it's better to mark dirty only having upper inode.
 > >
 > 
 > Yeh.
 > 
 > And since mapping_map_writable() is only called if VM_SHARED flag
 > is set (and not VM_MAYSHARE), we are not going to re-dirty an inode on
 > account of VM_MAYSHARE alone, so I wonder why we need to mark it
 > dirty here on account of VM_MAYSHARE?
 > 

Yeah, you are right. It just means the pages in this memory region can be mapped
by other process with shared+write mode and this is actually meaningless in our case.
So let's just ignore it. :-)


Thanks,
Chengguang




  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-08 14:02 [RFC PATCH v3 00/10] implement containerized syncfs for overlayfs Chengguang Xu
2020-11-08 14:02 ` [RFC PATCH v3 01/10] ovl: setup overlayfs' private bdi Chengguang Xu
2020-11-08 14:02 ` [RFC PATCH v3 02/10] ovl: introduce waiting list for syncfs Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 03/10] ovl: implement ->writepages operation Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 04/10] ovl: implement overlayfs' ->evict_inode operation Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 05/10] ovl: mark overlayfs' inode dirty on modification Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 06/10] ovl: mark overlayfs' inode dirty on shared mmap Chengguang Xu
2020-11-11 13:05   ` 回复:[RFC " Chengguang Xu
2020-11-11 15:20     ` [RFC " Amir Goldstein
2020-11-11 16:09       ` Chengguang Xu [this message]
2020-11-08 14:03 ` [RFC PATCH v3 07/10] ovl: implement overlayfs' ->write_inode operation Chengguang Xu
2020-11-10 13:45   ` Jan Kara
2020-11-10 15:12     ` Chengguang Xu
2020-11-11 10:54       ` Jan Kara
2020-11-10 16:18     ` Amir Goldstein
2020-11-08 14:03 ` [RFC PATCH v3 08/10] ovl: cache dirty overlayfs' inode Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 09/10] ovl: introduce helper of syncfs writeback inode waiting Chengguang Xu
2020-11-09  3:33   ` 回复:[RFC " Chengguang Xu
2020-11-09  7:07     ` [RFC " Amir Goldstein
2020-11-09  8:34       ` Chengguang Xu
2020-11-09 10:07         ` Amir Goldstein
2020-11-09 12:06           ` Chengguang Xu
2020-11-08 14:03 ` [RFC PATCH v3 10/10] ovl: implement containerized syncfs for overlayfs Chengguang Xu

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