Messages in this thread | | | Date | Thu, 7 Oct 2021 20:04:30 +0800 | Subject | Re: [RFC PATCH v5 07/10] ovl: cache dirty overlayfs' inode | From | Chengguang Xu <> |
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在 2021/10/7 19:09, Miklos Szeredi 写道: > On Thu, 23 Sept 2021 at 15:08, Chengguang Xu <cgxu519@mykernel.net> wrote: >> Now drop overlayfs' inode will sync dirty data, >> so we change to only drop clean inode. >> >> The purpose of doing this is to keep compatible >> behavior with before because without this change >> dropping overlayfs inode will not trigger syncing >> of underlying dirty inode. >> >> Signed-off-by: Chengguang Xu <cgxu519@mykernel.net> >> --- >> fs/overlayfs/super.c | 16 +++++++++++++++- >> 1 file changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c >> index cddae3ca2fa5..bf4000eb9be8 100644 >> --- a/fs/overlayfs/super.c >> +++ b/fs/overlayfs/super.c >> @@ -441,11 +441,25 @@ static int ovl_write_inode(struct inode *inode, >> return ret; >> } >> >> +/* >> + * In iput_final(), clean inode will drop directly and dirty inode will >> + * keep in the cache until write back to sync dirty data then add to lru >> + * list to wait reclaim. >> + */ >> +static int ovl_drop_inode(struct inode *inode) >> +{ >> + struct inode *upper = ovl_inode_upper(inode); >> + >> + if (!upper || !(inode->i_state & I_DIRTY_ALL)) > Could we check upper dirtyness here? That would give a more precise result.
We keep tracking mmapped-file(shared mode) by explicitely marking overlay inode dirty,
so if we drop overlay inode by checking upper dirtyness, we may lose control on those mmapped upper inodes.
> > Alternatively don't set .drop_inode (i.e. use generic_drop_inode()) > and set I_DONTCACHE on overlay inodes. That would cause the upper > inode to be always written back before eviction. > > The latter would result in simpler logic, and I think performance-wise > it wouldn't matter. But I may be missing something.
I think we may seperate mmapped-file(shared) inode and other inode by
clear/set I_DONTCACHE flag on overlay inode if you prefer this approach.
Thanks,
Chengguang
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