Re: [PATCH v13 03/10] xfs: Add delay ready attr set routines

Allison Henderson
2020-11-13T01:33:21Z

On 11/10/20 2:57 PM, Darrick J. Wong wrote:
> On Tue, Oct 27, 2020 at 07:02:55PM +0530, Chandan Babu R wrote:
>> On Friday 23 October 2020 12:04:28 PM IST Allison Henderson wrote:
>>> This patch modifies the attr set routines to be delay ready. This means
>>> they no longer roll or commit transactions, but instead return -EAGAIN
>>> to have the calling routine roll and refresh the transaction. In this
>>> series, xfs_attr_set_args has become xfs_attr_set_iter, which uses a
>>> state machine like switch to keep track of where it was when EAGAIN was
>>> returned. See xfs_attr.h for a more detailed diagram of the states.
>>>
>>> Two new helper functions have been added: xfs_attr_rmtval_set_init and
>>> xfs_attr_rmtval_set_blk. They provide a subset of logic similar to
>>> xfs_attr_rmtval_set, but they store the current block in the delay attr
>>> context to allow the caller to roll the transaction between allocations.
>>> This helps to simplify and consolidate code used by
>>> xfs_attr_leaf_addname and xfs_attr_node_addname. xfs_attr_set_args has
>>> now become a simple loop to refresh the transaction until the operation
>>> is completed. Lastly, xfs_attr_rmtval_remove is no longer used, and is
>>> removed.
>>
>> One nit. xfs_attr_rmtval_remove()'s prototype declaration needs to be removed
>> from xfs_attr_remote.h.
Alrighty, will pull out

>>
>>>
>>> Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
>>> ---
>>> fs/xfs/libxfs/xfs_attr.c | 370 ++++++++++++++++++++++++++--------------
>>> fs/xfs/libxfs/xfs_attr.h | 126 +++++++++++++-
>>> fs/xfs/libxfs/xfs_attr_remote.c | 99 +++++++----
>>> fs/xfs/libxfs/xfs_attr_remote.h | 4 +
>>> fs/xfs/xfs_trace.h | 1 -
>>> 5 files changed, 439 insertions(+), 161 deletions(-)
>>>
>>> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
>>> index 6ca94cb..95c98d7 100644
>>> --- a/fs/xfs/libxfs/xfs_attr.c
>>> +++ b/fs/xfs/libxfs/xfs_attr.c
>>> @@ -44,7 +44,7 @@ STATIC int xfs_attr_shortform_addname(xfs_da_args_t *args);
>>> * Internal routines when attribute list is one block.
>>> */
>>> STATIC int xfs_attr_leaf_get(xfs_da_args_t *args);
>>> -STATIC int xfs_attr_leaf_addname(xfs_da_args_t *args);
>>> +STATIC int xfs_attr_leaf_addname(struct xfs_delattr_context *dac);
>>> STATIC int xfs_attr_leaf_removename(xfs_da_args_t *args);
>>> STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
>>>
>>> @@ -52,12 +52,15 @@ STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
>>> * Internal routines when attribute list is more than one block.
>>> */
>>> STATIC int xfs_attr_node_get(xfs_da_args_t *args);
>>> -STATIC int xfs_attr_node_addname(xfs_da_args_t *args);
>>> +STATIC int xfs_attr_node_addname(struct xfs_delattr_context *dac);
>>> STATIC int xfs_attr_node_removename_iter(struct xfs_delattr_context *dac);
>>> STATIC int xfs_attr_node_hasname(xfs_da_args_t *args,
>>> struct xfs_da_state **state);
>>> STATIC int xfs_attr_fillstate(xfs_da_state_t *state);
>>> STATIC int xfs_attr_refillstate(xfs_da_state_t *state);
>>> +STATIC int xfs_attr_leaf_try_add(struct xfs_da_args *args, struct xfs_buf *bp);
>>> +STATIC int xfs_attr_set_iter(struct xfs_delattr_context *dac,
>>> + struct xfs_buf **leaf_bp);
>>>
>>> int
>>> xfs_inode_hasattr(
>>> @@ -218,8 +221,11 @@ xfs_attr_is_shortform(
>>>
>>> /*
>>> * Attempts to set an attr in shortform, or converts short form to leaf form if
>>> - * there is not enough room. If the attr is set, the transaction is committed
>>> - * and set to NULL.
>>> + * there is not enough room. This function is meant to operate as a helper
>>> + * routine to the delayed attribute functions. It returns -EAGAIN to indicate
>>> + * that the calling function should roll the transaction, and then proceed to
>>> + * add the attr in leaf form. This subroutine does not expect to be recalled
>>> + * again like the other delayed attr routines do.
>>> */
>>> STATIC int
>>> xfs_attr_set_shortform(
>>> @@ -227,16 +233,16 @@ xfs_attr_set_shortform(
>>> struct xfs_buf **leaf_bp)
>>> {
>>> struct xfs_inode *dp = args->dp;
>>> - int error, error2 = 0;
>>> + int error = 0;
>>>
>>> /*
>>> * Try to add the attr to the attribute list in the inode.
>>> */
>>> error = xfs_attr_try_sf_addname(dp, args);
>>> +
>>> + /* Should only be 0, -EEXIST or ENOSPC */
>>> if (error != -ENOSPC) {
>>> - error2 = xfs_trans_commit(args->trans);
>>> - args->trans = NULL;
>>> - return error ? error : error2;
>>> + return error;
>>> }
>>> /*
>>> * It won't fit in the shortform, transform to a leaf block. GROT:
>>> @@ -249,18 +255,10 @@ xfs_attr_set_shortform(
>>> /*
>>> * Prevent the leaf buffer from being unlocked so that a concurrent AIL
>>> * push cannot grab the half-baked leaf buffer and run into problems
>>> - * with the write verifier. Once we're done rolling the transaction we
>>> - * can release the hold and add the attr to the leaf.
>>> + * with the write verifier.
>>> */
>>> xfs_trans_bhold(args->trans, *leaf_bp);
>>> - error = xfs_defer_finish(&args->trans);
>>> - xfs_trans_bhold_release(args->trans, *leaf_bp);
>>> - if (error) {
>>> - xfs_trans_brelse(args->trans, *leaf_bp);
>>> - return error;
>>> - }
>>> -
>>> - return 0;
>>> + return -EAGAIN;
>>> }
>>>
>>> /*
>>> @@ -268,7 +266,7 @@ xfs_attr_set_shortform(
>>> * also checks for a defer finish. Transaction is finished and rolled as
>>> * needed, and returns true of false if the delayed operation should continue.
>>> */
>>> -int
>>> +STATIC int
>>> xfs_attr_trans_roll(
>>> struct xfs_delattr_context *dac)
>>> {
>>> @@ -297,61 +295,130 @@ int
>>> xfs_attr_set_args(
>>> struct xfs_da_args *args)
>>> {
>>> - struct xfs_inode *dp = args->dp;
>>> - struct xfs_buf *leaf_bp = NULL;
>>> - int error = 0;
>>> + struct xfs_buf *leaf_bp = NULL;
>>> + int error = 0;
>>> + struct xfs_delattr_context dac = {
>>> + .da_args = args,
>>> + };
>>> +
>>> + do {
>>> + error = xfs_attr_set_iter(&dac, &leaf_bp);
>>> + if (error != -EAGAIN)
>>> + break;
>>> +
>>> + error = xfs_attr_trans_roll(&dac);
>>> + if (error)
>>> + return error;
>>> +
>>> + if (leaf_bp) {
>>> + xfs_trans_bjoin(args->trans, leaf_bp);
>>> + xfs_trans_bhold(args->trans, leaf_bp);
>>> + }
>>
>> When xfs_attr_set_iter() causes a "short form" attribute list to be converted
>> to "leaf form", leaf_bp would point to an xfs_buf which has been added to the
>> transaction and also XFS_BLI_HOLD flag is set on the buffer (last statement in
>> xfs_attr_set_shortform()). XFS_BLI_HOLD flag makes sure that the new
>> transaction allocated by xfs_attr_trans_roll() would continue to have leaf_bp
>> in the transaction's item list. Hence I think the above calls to
>> xfs_trans_bjoin() and xfs_trans_bhold() are not required.
Sorry, I just noticed Chandans commentary for this patch. Apologies. I
think we can get away with out this now, but yes this routine disappears
at the end of the set now. Will clean out anyway for bisecting reasons
though. :-)

>
> I /think/ the defer ops will rejoin the buffer each time it rolls, which
> means that xfs_attr_trans_roll returns with the buffer already joined to
> the transaction? And I think you're right that the bhold isn't needed,
> because holding is dictated by the lower levels (i.e. _set_iter).
>
>> Please let me know if I am missing something obvious here.
>
> The entire function goes away by the end of the series. :)
>
> --D
>
>>
>> --
>> chandan
>>
>>
>>