On Tue, Oct 27, 2020 at 03:27:20PM -0700, Allison Henderson wrote:
>
>
> On 10/27/20 5:16 AM, 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@xxxxxxxxxx>
> > > ---
> > > 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
...
> > > @@ -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://urldefense.com/v3/__https://lore.kernel.org/linux-xfs/20200901170020.GC174813@bfoster/__;!!GqivPVa7Brio!JKxU3Z07HVj0V1YFesXrveRWnoGuWqiTZuaIDiG9UFmSxz-aFGsZPpLtjIOjSht7WL_h$
> >
> > 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.
> >
> > Brian
>
> Yes, I did see the pseudo code, though I wasnt able to get it through the
> test cases quite the way it appears. Because whether or not we proceed to
> shrink is determined by the leaf remove that's burried in the step function.
> Otherwise we run into some failed asserts in the shrink routines for
> "state->path.active == 1". Alternatly we can add another helper to pull it
> up to this scope. Then the switch ends up looking like this:
>
Ok. That was more focused on just showing an approach that collects all
of the state transition logic in one place. The factoring below seems
generally reasonable to me..
> switch (dac->dela_state) {
>
> case XFS_DAS_UNINIT:
>
> /*
>
> * repeatedly remove remote blocks, remove the entry and
> * join. returns -EAGAIN or 0 for completion of the step.
> */
>
> error = xfs_attr_node_remove_step(dac);
>
> if (error)
>
> break;
>
>
>
> retval = xfs_attr_node_remove_cleanup(dac);
>
>
>
> /*
>
> * Check to see if the tree needs to be collapsed. Set the
> flag to
> * indicate that the calling function needs to move the to
> shrink
> * operation
>
> */
>
> if (retval && (state->path.active > 1)) {
>
> error = xfs_da3_join(state);
>
> if (error)
>
> return error;
>
>
>
> dac->dela_state = XFS_DAS_RM_SHRINK;
>
> return -EAGAIN;
>
> }
>
>
>
> /* check whether to shrink or return success */
>
> if (!error && xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
>
> dac->dela_state = XFS_DAS_RM_SHRINK;
>
> error = -EAGAIN;
>
> }
... though what is the purpose of this hunk? This seems to diverge from
the current logic, but maybe I'm missing something.
>
> break;
>
> case XFS_DAS_RM_SHRINK:
>
> /*
>
> * If the result is small enough, push it all into the
> inode.
> */
>
> error = xfs_attr_node_shrink(args, state);
>
>
>
> break;
>
> default:
>
> ASSERT(0);
>
> return -EINVAL;
>
> }
>
>
>
> if (error == -EAGAIN)
>
> return error;
>
>
>
>
>
> And then we have this little clean up helper that we pull out of
> remove_step:
>
>
>
> STATIC int
>
> xfs_attr_node_remove_cleanup(
>
> struct xfs_delattr_context *dac)
>
> {
>
> struct xfs_da_args *args = dac->da_args;
>
> struct xfs_da_state_blk *blk;
>
> int retval;
>
>
>
> /*
>
> * Remove the name and update the hashvals in the tree.
>
> */
>
> blk = &dac->da_state->path.blk[ dac->da_state->path.active-1 ];
>
> ASSERT(blk->magic == XFS_ATTR_LEAF_MAGIC);
>
> retval = xfs_attr3_leaf_remove(blk->bp, args);
>
> xfs_da3_fixhashpath(dac->da_state, &dac->da_state->path);
>
>
>
> return retval;
>
> }
>
>
> This configuration seems to get through the test cases. It's not quite as
> tidy, but it does get all the state handling into this scope. If people
> prefer it this way I can add in the extra helper and make these adjustments?
>
Makes sense. I think the goal should be to pull the state management
into one (or as few) place(s) as technically possible and we should
refactor however necessary to accomplish that (please just pull the
refactoring out into preliminary patches to facilitate review). Thanks.
Brian
> Allison
>
> >
> > > - /*
> > > - * 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
> > >
> >
>
