Re: [PATCH v13 02/10] xfs: Add delay ready attr remove routines

Darrick J. Wong
2020-11-10T23:17:59Z

On Tue, Oct 27, 2020 at 08:16:45AM -0400, Brian Foster wrote:
> On Thu, Oct 22, 2020 at 11:34:27PM -0700, Allison Henderson wrote:
> > This patch modifies the attr remove 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_remove_args has become xfs_attr_remove_iter, which
> > uses a sort of state machine like switch to keep track of where it was
> > when EAGAIN was returned. xfs_attr_node_removename has also been
> > modified to use the switch, and a new version of xfs_attr_remove_args
> > consists of a simple loop to refresh the transaction until the operation
> > is completed. A new XFS_DAC_DEFER_FINISH flag is used to finish the
> > transaction where ever the existing code used to.
> >
> > Calls to xfs_attr_rmtval_remove are replaced with the delay ready
> > version __xfs_attr_rmtval_remove. We will rename
> > __xfs_attr_rmtval_remove back to xfs_attr_rmtval_remove when we are
> > done.
> >
> > xfs_attr_rmtval_remove itself is still in use by the set routines (used
> > during a rename). For reasons of preserving existing function, we
> > modify xfs_attr_rmtval_remove to call xfs_defer_finish when the flag is
> > set. Similar to how xfs_attr_remove_args does here. Once we transition
> > the set routines to be delay ready, xfs_attr_rmtval_remove is no longer
> > used and will be removed.
> >
> > This patch also adds a new struct xfs_delattr_context, which we will use
> > to keep track of the current state of an attribute operation. The new
> > xfs_delattr_state enum is used to track various operations that are in
> > progress so that we know not to repeat them, and resume where we left
> > off before EAGAIN was returned to cycle out the transaction. Other
> > members take the place of local variables that need to retain their
> > values across multiple function recalls. See xfs_attr.h for a more
> > detailed diagram of the states.
> >
> > Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> > ---
> > fs/xfs/libxfs/xfs_attr.c | 200 +++++++++++++++++++++++++++++-----------
> > fs/xfs/libxfs/xfs_attr.h | 72 +++++++++++++++
> > fs/xfs/libxfs/xfs_attr_leaf.c | 2 +-
> > fs/xfs/libxfs/xfs_attr_remote.c | 37 ++++----
> > fs/xfs/libxfs/xfs_attr_remote.h | 2 +-
> > fs/xfs/xfs_attr_inactive.c | 2 +-
> > 6 files changed, 241 insertions(+), 74 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > index f4d39bf..6ca94cb 100644
> > --- a/fs/xfs/libxfs/xfs_attr.c
> > +++ b/fs/xfs/libxfs/xfs_attr.c
<snip>
> > @@ -1282,31 +1356,53 @@ xfs_attr_node_remove_step(
> > *
> > * This routine will find the blocks of the name to remove, remove them and
> > * shirnk the tree if needed.
> > + *
> > + * This routine is meant to function as either an inline or delayed operation,
> > + * and may return -EAGAIN when the transaction needs to be rolled. Calling
> > + * functions will need to handle this, and recall the function until a
> > + * successful error code is returned.
> > */
> > STATIC int
> > -xfs_attr_node_removename(
> > - struct xfs_da_args *args)
> > +xfs_attr_node_removename_iter(
> > + struct xfs_delattr_context *dac)
> > {
> > - struct xfs_da_state *state;
> > - int error;
> > - struct xfs_inode *dp = args->dp;
> > + struct xfs_da_args *args = dac->da_args;
> > + struct xfs_da_state *state;
> > + int error;
> > + struct xfs_inode *dp = args->dp;
> >
> > trace_xfs_attr_node_removename(args);
> > + state = dac->da_state;
> >
> > - error = xfs_attr_node_removename_setup(args, &state);
> > - if (error)
> > - goto out;
> > + if ((dac->flags & XFS_DAC_NODE_RMVNAME_INIT) == 0) {
> > + dac->flags |= XFS_DAC_NODE_RMVNAME_INIT;
> > + error = xfs_attr_node_removename_setup(dac, &state);
> > + if (error)
> > + goto out;
> > + }
> >
> > - error = xfs_attr_node_remove_step(args, state);
> > - if (error)
> > - goto out;
> > + switch (dac->dela_state) {
> > + case XFS_DAS_UNINIT:
> > + error = xfs_attr_node_remove_step(dac);
> > + if (error)
> > + break;
> >
>
> I think there's a bit more preliminary refactoring to do here to isolate
> the state management to this one function. I.e., from the discussion on
> the previous version, we'd ideally pull the logic that checks for the
> subsequent shrink state out of xfs_attr_node_remove_step() and lift it
> into this branch. See the pseudocode in the previous discussion for an
> example of what I mean:
>
> https://lore.kernel.org/linux-xfs/20200901170020.GC174813@bfoster/
>
> The general goal of that is to refactor the existing code such that all
> of the state transitions and whatnot are shown in one place and the rest
> is broken down into smaller functional helpers.

Agreed.

--D

> Brian
>
> > - /*
> > - * If the result is small enough, push it all into the inode.
> > - */
> > - if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> > - error = xfs_attr_node_shrink(args, state);
> > + /* do not break, proceed to shrink if needed */
> > + case XFS_DAS_RM_SHRINK:
> > + /*
> > + * If the result is small enough, push it all into the inode.
> > + */
> > + if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
> > + error = xfs_attr_node_shrink(args, state);
> >
> > + break;
> > + default:
> > + ASSERT(0);
> > + return -EINVAL;
> > + }
> > +
> > + if (error == -EAGAIN)
> > + return error;
> > out:
> > if (state)
> > xfs_da_state_free(state);
> > diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> > index 3e97a93..64dcf0f 100644
> > --- a/fs/xfs/libxfs/xfs_attr.h
> > +++ b/fs/xfs/libxfs/xfs_attr.h
> > @@ -74,6 +74,74 @@ struct xfs_attr_list_context {
> > };
> >
> >
> > +/*
> > + * ========================================================================
> > + * Structure used to pass context around among the delayed routines.
> > + * ========================================================================
> > + */
> > +
> > +/*
> > + * Below is a state machine diagram for attr remove operations. The XFS_DAS_*
> > + * states indicate places where the function would return -EAGAIN, and then
> > + * immediately resume from after being recalled by the calling function. States
> > + * marked as a "subroutine state" indicate that they belong to a subroutine, and
> > + * so the calling function needs to pass them back to that subroutine to allow
> > + * it to finish where it left off. But they otherwise do not have a role in the
> > + * calling function other than just passing through.
> > + *
> > + * xfs_attr_remove_iter()
> > + * XFS_DAS_RM_SHRINK ─┐
> > + * (subroutine state) │
> > + * └─>xfs_attr_node_removename()
> > + * │
> > + * v
> > + * need to
> > + * shrink tree? ─n─┐
> > + * │ │
> > + * y │
> > + * │ │
> > + * v │
> > + * XFS_DAS_RM_SHRINK │
> > + * │ │
> > + * v │
> > + * done <─────┘
> > + *
> > + */
> > +
> > +/*
> > + * Enum values for xfs_delattr_context.da_state
> > + *
> > + * These values are used by delayed attribute operations to keep track of where
> > + * they were before they returned -EAGAIN. A return code of -EAGAIN signals the
> > + * calling function to roll the transaction, and then recall the subroutine to
> > + * finish the operation. The enum is then used by the subroutine to jump back
> > + * to where it was and resume executing where it left off.
> > + */
> > +enum xfs_delattr_state {
> > + XFS_DAS_UNINIT = 0, /* No state has been set yet */
> > + XFS_DAS_RM_SHRINK, /* We are shrinking the tree */
> > +};
> > +
> > +/*
> > + * Defines for xfs_delattr_context.flags
> > + */
> > +#define XFS_DAC_DEFER_FINISH 0x01 /* finish the transaction */
> > +#define XFS_DAC_NODE_RMVNAME_INIT 0x02 /* xfs_attr_node_removename init */
> > +
> > +/*
> > + * Context used for keeping track of delayed attribute operations
> > + */
> > +struct xfs_delattr_context {
> > + struct xfs_da_args *da_args;
> > +
> > + /* Used in xfs_attr_node_removename to roll through removing blocks */
> > + struct xfs_da_state *da_state;
> > +
> > + /* Used to keep track of current state of delayed operation */
> > + unsigned int flags;
> > + enum xfs_delattr_state dela_state;
> > +};
> > +
> > /*========================================================================
> > * Function prototypes for the kernel.
> > *========================================================================*/
> > @@ -91,6 +159,10 @@ int xfs_attr_set(struct xfs_da_args *args);
> > int xfs_attr_set_args(struct xfs_da_args *args);
> > int xfs_has_attr(struct xfs_da_args *args);
> > int xfs_attr_remove_args(struct xfs_da_args *args);
> > +int xfs_attr_remove_iter(struct xfs_delattr_context *dac);
> > +int xfs_attr_trans_roll(struct xfs_delattr_context *dac);
> > bool xfs_attr_namecheck(const void *name, size_t length);
> > +void xfs_delattr_context_init(struct xfs_delattr_context *dac,
> > + struct xfs_da_args *args);
> >
> > #endif /* __XFS_ATTR_H__ */
> > diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> > index bb128db..338377e 100644
> > --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> > +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> > @@ -19,8 +19,8 @@
> > #include "xfs_bmap_btree.h"
> > #include "xfs_bmap.h"
> > #include "xfs_attr_sf.h"
> > -#include "xfs_attr_remote.h"
> > #include "xfs_attr.h"
> > +#include "xfs_attr_remote.h"
> > #include "xfs_attr_leaf.h"
> > #include "xfs_error.h"
> > #include "xfs_trace.h"
> > diff --git a/fs/xfs/libxfs/xfs_attr_remote.c b/fs/xfs/libxfs/xfs_attr_remote.c
> > index 48d8e9c..1426c15 100644
> > --- a/fs/xfs/libxfs/xfs_attr_remote.c
> > +++ b/fs/xfs/libxfs/xfs_attr_remote.c
> > @@ -674,10 +674,12 @@ xfs_attr_rmtval_invalidate(
> > */
> > int
> > xfs_attr_rmtval_remove(
> > - struct xfs_da_args *args)
> > + struct xfs_da_args *args)
> > {
> > - int error;
> > - int retval;
> > + int error;
> > + struct xfs_delattr_context dac = {
> > + .da_args = args,
> > + };
> >
> > trace_xfs_attr_rmtval_remove(args);
> >
> > @@ -685,19 +687,17 @@ xfs_attr_rmtval_remove(
> > * Keep de-allocating extents until the remote-value region is gone.
> > */
> > do {
> > - retval = __xfs_attr_rmtval_remove(args);
> > - if (retval && retval != -EAGAIN)
> > - return retval;
> > + error = __xfs_attr_rmtval_remove(&dac);
> > + if (error != -EAGAIN)
> > + break;
> >
> > - /*
> > - * Close out trans and start the next one in the chain.
> > - */
> > - error = xfs_trans_roll_inode(&args->trans, args->dp);
> > + error = xfs_attr_trans_roll(&dac);
> > if (error)
> > return error;
> > - } while (retval == -EAGAIN);
> >
> > - return 0;
> > + } while (true);
> > +
> > + return error;
> > }
> >
> > /*
> > @@ -707,9 +707,10 @@ xfs_attr_rmtval_remove(
> > */
> > int
> > __xfs_attr_rmtval_remove(
> > - struct xfs_da_args *args)
> > + struct xfs_delattr_context *dac)
> > {
> > - int error, done;
> > + struct xfs_da_args *args = dac->da_args;
> > + int error, done;
> >
> > /*
> > * Unmap value blocks for this attr.
> > @@ -719,12 +720,10 @@ __xfs_attr_rmtval_remove(
> > if (error)
> > return error;
> >
> > - error = xfs_defer_finish(&args->trans);
> > - if (error)
> > - return error;
> > -
> > - if (!done)
> > + if (!done) {
> > + dac->flags |= XFS_DAC_DEFER_FINISH;
> > return -EAGAIN;
> > + }
> >
> > return error;
> > }
> > diff --git a/fs/xfs/libxfs/xfs_attr_remote.h b/fs/xfs/libxfs/xfs_attr_remote.h
> > index 9eee615..002fd30 100644
> > --- a/fs/xfs/libxfs/xfs_attr_remote.h
> > +++ b/fs/xfs/libxfs/xfs_attr_remote.h
> > @@ -14,5 +14,5 @@ int xfs_attr_rmtval_remove(struct xfs_da_args *args);
> > int xfs_attr_rmtval_stale(struct xfs_inode *ip, struct xfs_bmbt_irec *map,
> > xfs_buf_flags_t incore_flags);
> > int xfs_attr_rmtval_invalidate(struct xfs_da_args *args);
> > -int __xfs_attr_rmtval_remove(struct xfs_da_args *args);
> > +int __xfs_attr_rmtval_remove(struct xfs_delattr_context *dac);
> > #endif /* __XFS_ATTR_REMOTE_H__ */
> > diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c
> > index bfad669..aaa7e66 100644
> > --- a/fs/xfs/xfs_attr_inactive.c
> > +++ b/fs/xfs/xfs_attr_inactive.c
> > @@ -15,10 +15,10 @@
> > #include "xfs_da_format.h"
> > #include "xfs_da_btree.h"
> > #include "xfs_inode.h"
> > +#include "xfs_attr.h"
> > #include "xfs_attr_remote.h"
> > #include "xfs_trans.h"
> > #include "xfs_bmap.h"
> > -#include "xfs_attr.h"
> > #include "xfs_attr_leaf.h"
> > #include "xfs_quota.h"
> > #include "xfs_dir2.h"
> > --
> > 2.7.4
> >
>