Re: [RFC PATCH v3] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

Shiyang Ruan
2022-06-24T01:51:23Z

在 2022/6/23 0:49, Darrick J. Wong 写道:
> On Wed, Jun 15, 2022 at 08:54:00PM +0800, Shiyang Ruan wrote:
>> This patch is inspired by Dan's "mm, dax, pmem: Introduce
>> dev_pagemap_failure()"[1]. With the help of dax_holder and
>> ->notify_failure() mechanism, the pmem driver is able to ask filesystem
>> (or mapped device) on it to unmap all files in use and notify processes
>> who are using those files.
>>
>> Call trace:
>> trigger unbind
>> -> unbind_store()
>> -> ... (skip)
>> -> devres_release_all() # was pmem driver ->remove() in v1
>> -> kill_dax()
>> -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_REMOVE)
>> -> xfs_dax_notify_failure()
>>
>> Introduce MF_MEM_REMOVE to let filesystem know this is a remove event.
>> So do not shutdown filesystem directly if something not supported, or if
>> failure range includes metadata area. Make sure all files and processes
>> are handled correctly.
>>
>> [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
>>
>> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
>>
>> ==
>> Changes since v2:
>> 1. Rebased on next-20220615
>>
>> Changes since v1:
>> 1. Drop the needless change of moving {kill,put}_dax()
>> 2. Rebased on '[PATCHSETS] v14 fsdax-rmap + v11 fsdax-reflink'[2]
>>
>> ---
>> drivers/dax/super.c | 2 +-
>> fs/xfs/xfs_notify_failure.c | 6 +++++-
>> include/linux/mm.h | 1 +
>> 3 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
>> index 9b5e2a5eb0ae..d4bc83159d46 100644
>> --- a/drivers/dax/super.c
>> +++ b/drivers/dax/super.c
>> @@ -323,7 +323,7 @@ void kill_dax(struct dax_device *dax_dev)
>> return;
>>
>> if (dax_dev->holder_data != NULL)
>> - dax_holder_notify_failure(dax_dev, 0, U64_MAX, 0);
>> + dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_REMOVE);
>
> At the point we're initiating a MEM_REMOVE call, is the pmem already
> gone, or is it about to be gone?

It's about to be gone.

I found two cases:
1. exec `unbind` by user, who wants to unplug the pmem
2. handle failures during initialization

>
>>
>> clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
>> synchronize_srcu(&dax_srcu);
>> diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
>> index aa8dc27c599c..91d3f05d4241 100644
>> --- a/fs/xfs/xfs_notify_failure.c
>> +++ b/fs/xfs/xfs_notify_failure.c
>> @@ -73,7 +73,9 @@ xfs_dax_failure_fn(
>> struct failure_info *notify = data;
>> int error = 0;
>>
>> - if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
>> + /* Do not shutdown so early when device is to be removed */
>> + if (!(notify->mf_flags & MF_MEM_REMOVE) ||
>> + XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
>> (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
>> xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
>> return -EFSCORRUPTED;
>> @@ -182,6 +184,8 @@ xfs_dax_notify_failure(
>>
>> if (mp->m_logdev_targp && mp->m_logdev_targp->bt_daxdev == dax_dev &&
>> mp->m_logdev_targp != mp->m_ddev_targp) {
>> + if (mf_flags & MF_MEM_REMOVE)
>> + return -EOPNOTSUPP;
>
> The reason I ask is that if the pmem is *about to be* but not yet
> removed from the system, shouldn't we at least try to flush all dirty
> files and the log to reduce data loss and minimize recovery time?

Yes, they should be flushed. Will add it.

--
Thanks,
Ruan.

>
> If it's already gone, then you might as well shut down immediately,
> unless there's a chance the pmem will come back(?)
>
> --D
>
>> xfs_err(mp, "ondisk log corrupt, shutting down fs!");
>> xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
>> return -EFSCORRUPTED;
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 623c2ee8330a..bbeb31883362 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3249,6 +3249,7 @@ enum mf_flags {
>> MF_SOFT_OFFLINE = 1 << 3,
>> MF_UNPOISON = 1 << 4,
>> MF_NO_RETRY = 1 << 5,
>> + MF_MEM_REMOVE = 1 << 6,
>> };
>> int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>> unsigned long count, int mf_flags);
>> --
>> 2.36.1
>>
>>
>>