On Thu, Sep 29, 2016 at 12:03:45PM -0700, Darrick J. Wong wrote:
> On Thu, Sep 29, 2016 at 10:44:33AM -0400, Brian Foster wrote:
> > On Tue, Sep 27, 2016 at 07:54:46PM -0700, Darrick J. Wong wrote:
> > > Provide functions to adjust the reference counts for an extent of
> > > physical blocks stored in the refcount btree.
> > >
> > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > > ---
> > > v2: Refactor the left/right split code into a single function. Track
> > > the number of btree shape changes and record updates during a refcount
> > > update so that we can decide if we need to get a fresh transaction to
> > > continue.
> > > ---
> > > fs/xfs/libxfs/xfs_refcount.c | 783 ++++++++++++++++++++++++++++++++++++++++++
> > > fs/xfs/xfs_error.h | 4
> > > 2 files changed, 786 insertions(+), 1 deletion(-)
> > >
> > >
> > > diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c
> > > index de13406..4f82651 100644
> > > --- a/fs/xfs/libxfs/xfs_refcount.c
> > > +++ b/fs/xfs/libxfs/xfs_refcount.c
> > > @@ -37,6 +37,12 @@
> > > #include "xfs_bit.h"
> > > #include "xfs_refcount.h"
> > >
> > > +/* Allowable refcount adjustment amounts. */
> > > +enum xfs_refc_adjust_op {
> > > + XFS_REFCOUNT_ADJUST_INCREASE = 1,
> > > + XFS_REFCOUNT_ADJUST_DECREASE = -1,
> > > +};
> > > +
> > > /*
> > > * Look up the first record less than or equal to [bno, len] in the btree
> > > * given by cur.
> > > @@ -175,3 +181,780 @@ xfs_refcount_delete(
> > > cur->bc_private.a.agno, error, _RET_IP_);
> > > return error;
> > > }
> > > +
> > > +/*
> > > + * Adjusting the Reference Count
> > > + *
> > > + * As stated elsewhere, the reference count btree (refcbt) stores
> > > + * >1 reference counts for extents of physical blocks. In this
> > > + * operation, we're either raising or lowering the reference count of
> > > + * some subrange stored in the tree:
> > > + *
> > > + * <------ adjustment range ------>
> > > + * ----+ +---+-----+ +--+--------+---------
> > > + * 2 | | 3 | 4 | |17| 55 | 10
> > > + * ----+ +---+-----+ +--+--------+---------
> > > + * X axis is physical blocks number;
> > > + * reference counts are the numbers inside the rectangles
> > > + *
> > > + * The first thing we need to do is to ensure that there are no
> > > + * refcount extents crossing either boundary of the range to be
> > > + * adjusted. For any extent that does cross a boundary, split it into
> > > + * two extents so that we can increment the refcount of one of the
> > > + * pieces later:
> > > + *
> > > + * <------ adjustment range ------>
> > > + * ----+ +---+-----+ +--+--------+----+----
> > > + * 2 | | 3 | 2 | |17| 55 | 10 | 10
> > > + * ----+ +---+-----+ +--+--------+----+----
> > > + *
> > > + * For this next step, let's assume that all the physical blocks in
> > > + * the adjustment range are mapped to a file and are therefore in use
> > > + * at least once. Therefore, we can infer that any gap in the
> > > + * refcount tree within the adjustment range represents a physical
> > > + * extent with refcount == 1:
> > > + *
> > > + * <------ adjustment range ------>
> > > + * ----+---+---+-----+-+--+--------+----+----
> > > + * 2 |"1"| 3 | 2 |1|17| 55 | 10 | 10
> > > + * ----+---+---+-----+-+--+--------+----+----
> > > + * ^
> > > + *
> > > + * For each extent that falls within the interval range, figure out
> > > + * which extent is to the left or the right of that extent. Now we
> > > + * have a left, current, and right extent. If the new reference count
> > > + * of the center extent enables us to merge left, center, and right
> > > + * into one record covering all three, do so. If the center extent is
> > > + * at the left end of the range, abuts the left extent, and its new
> > > + * reference count matches the left extent's record, then merge them.
> > > + * If the center extent is at the right end of the range, abuts the
> > > + * right extent, and the reference counts match, merge those. In the
> > > + * example, we can left merge (assuming an increment operation):
> > > + *
> > > + * <------ adjustment range ------>
> > > + * --------+---+-----+-+--+--------+----+----
> > > + * 2 | 3 | 2 |1|17| 55 | 10 | 10
> > > + * --------+---+-----+-+--+--------+----+----
> > > + * ^
> > > + *
> > > + * For all other extents within the range, adjust the reference count
> > > + * or delete it if the refcount falls below 2. If we were
> > > + * incrementing, the end result looks like this:
> > > + *
> > > + * <------ adjustment range ------>
> > > + * --------+---+-----+-+--+--------+----+----
> > > + * 2 | 4 | 3 |2|18| 56 | 11 | 10
> > > + * --------+---+-----+-+--+--------+----+----
> > > + *
> > > + * The result of a decrement operation looks as such:
> > > + *
> > > + * <------ adjustment range ------>
> > > + * ----+ +---+ +--+--------+----+----
> > > + * 2 | | 2 | |16| 54 | 9 | 10
> > > + * ----+ +---+ +--+--------+----+----
> > > + * DDDD 111111DD
> > > + *
> > > + * The blocks marked "D" are freed; the blocks marked "1" are only
> > > + * referenced once and therefore the record is removed from the
> > > + * refcount btree.
> > > + */
> > > +
> >
> > Thanks for the big comment. It makes this much easier to follow.
>
> NP. :)
>
> > > +#define RCNEXT(rc) ((rc).rc_startblock + (rc).rc_blockcount)
> > ...
> > > +/*
> > > + * Merge the left, center, and right extents.
> > > + */
> > > +STATIC int
> > > +xfs_refcount_merge_center_extent(
> > > + struct xfs_btree_cur *cur,
> > > + struct xfs_refcount_irec *left,
> > > + struct xfs_refcount_irec *center,
> > > + unsigned long long extlen,
> > > + xfs_agblock_t *agbno,
> > > + xfs_extlen_t *aglen)
> > > +{
> > > + int error;
> > > + int found_rec;
> > > +
> > > + error = xfs_refcount_lookup_ge(cur, center->rc_startblock,
> > > + &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
> > > +
> > > + error = xfs_refcount_delete(cur, &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
> > > +
> > > + if (center->rc_refcount > 1) {
> >
> > Comment please :) (what is special about refcount == 1?).
>
> /*
> * If the center extent wasn't synthesized, remove it. See the comments
> * in _reflink_find_left_extents explaining when this is possible.
> */
>
I get the idea, but that doesn't exactly sound like what the code is
doing. If the center extent wasn't synthesized, we've deleted it in the
call above.
> and updated comments in _reflink_find_{left,right}_extents:
>
> /*
> * There's a gap in the refcntbt at the start of the range we're
> * interested in (refcount == 1) so synthesize the implied extent and
> * pass it back. We assume here that the agbno/aglen range was passed
> * in from a data fork extent mapping and therefore is allocated to
> * exactly one owner.
> */
>
Sounds good, thanks.
> > > + error = xfs_refcount_delete(cur, &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1,
> > > + out_error);
> > > + }
> > > +
> > > + error = xfs_refcount_lookup_le(cur, left->rc_startblock,
> > > + &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + XFS_WANT_CORRUPTED_GOTO(cur->bc_mp, found_rec == 1, out_error);
> > > +
> > > + left->rc_blockcount = extlen;
> >
> > Is extlen valid if the (refcount > 1) condition above fails? Digging
> > further, I suppose so as the refcount == 1 case appears to be a
> > filler/non-existent extent..?
>
> Right.
>
> > > + error = xfs_refcount_update(cur, left);
> > > + if (error)
> > > + goto out_error;
> > > +
> > > + *aglen = 0;
> > > + return error;
> > > +
> > > +out_error:
> > > + trace_xfs_refcount_merge_center_extents_error(cur->bc_mp,
> > > + cur->bc_private.a.agno, error, _RET_IP_);
> > > + return error;
> > > +}
> > > +
> > ...
> > > +/*
> > > + * Try to merge with any extents on the boundaries of the adjustment range.
> > > + */
> > > +STATIC int
> > > +xfs_refcount_merge_extents(
> > > + struct xfs_btree_cur *cur,
> > > + xfs_agblock_t *agbno,
> > > + xfs_extlen_t *aglen,
> > > + enum xfs_refc_adjust_op adjust,
> > > + bool *shape_changed)
> > > +{
> > > + struct xfs_refcount_irec left = {0}, cleft = {0};
> > > + struct xfs_refcount_irec cright = {0}, right = {0};
> > > + int error;
> > > + unsigned long long ulen;
> > > + bool cequal;
> > > +
> > > + *shape_changed = false;
> > > + /*
> > > + * Find the extent just below agbno [left], just above agbno [cleft],
> > > + * just below (agbno + aglen) [cright], and just above (agbno + aglen)
> > > + * [right].
> > > + */
> > > + error = xfs_refcount_find_left_extents(cur, &left, &cleft, *agbno,
> > > + *aglen);
> > > + if (error)
> > > + return error;
> > > + error = xfs_refcount_find_right_extents(cur, &right, &cright, *agbno,
> > > + *aglen);
> > > + if (error)
> > > + return error;
> > > +
> > > + /* No left or right extent to merge; exit. */
> > > + if (left.rc_blockcount == 0 && right.rc_blockcount == 0)
> > > + return 0;
> >
> > Can we use start block and NULLAGBLOCK in the find helpers to identify
> > the no extent case rather than blockcount == 0?
>
> Yes, that makes more sense.
>
> > > +
> > > + *shape_changed = true;
> >
> > Why is this true already if we haven't actually merged extents yet? This
> > could use some explanation...
>
> Overly conservative estimate of whether or not refcount extents got
> inserted or deleted. This will get moved to just prior to the
> _refcount_merge_*_extents calls.
>
Ok.
> > > + cequal = (cleft.rc_startblock == cright.rc_startblock) &&
> > > + (cleft.rc_blockcount == cright.rc_blockcount);
> > > +
> > > + /* Try to merge left, cleft, and right. cleft must == cright. */
> > > + ulen = (unsigned long long)left.rc_blockcount + cleft.rc_blockcount +
> > > + right.rc_blockcount;
> > > + if (left.rc_blockcount != 0 && right.rc_blockcount != 0 &&
> > > + cleft.rc_blockcount != 0 && cright.rc_blockcount != 0 &&
> > > + cequal &&
> > > + left.rc_refcount == cleft.rc_refcount + adjust &&
> > > + right.rc_refcount == cleft.rc_refcount + adjust &&
> > > + ulen < MAXREFCEXTLEN) {
> > > + trace_xfs_refcount_merge_center_extents(cur->bc_mp,
> > > + cur->bc_private.a.agno, &left, &cleft, &right);
> >
> > I'd suggest to bury tracepoints such as this (generally speaking, those
> > that match a function name) down into the start of the associated
> > function rather than at the call site. That seems more consistent with
> > the rest of XFS.
>
> Ok. I should've moved them when I refactored all those bits into
> separate functions long ago.
>
> >
> > > + return xfs_refcount_merge_center_extent(cur, &left, &cleft,
> > > + ulen, agbno, aglen);
> > > + }
> > > +
> > > + /* Try to merge left and cleft. */
> > > + ulen = (unsigned long long)left.rc_blockcount + cleft.rc_blockcount;
> > > + if (left.rc_blockcount != 0 && cleft.rc_blockcount != 0 &&
> > > + left.rc_refcount == cleft.rc_refcount + adjust &&
> > > + ulen < MAXREFCEXTLEN) {
> > > + trace_xfs_refcount_merge_left_extent(cur->bc_mp,
> > > + cur->bc_private.a.agno, &left, &cleft);
> > > + error = xfs_refcount_merge_left_extent(cur, &left, &cleft,
> > > + agbno, aglen);
> > > + if (error)
> > > + return error;
> > > +
> > > + /*
> > > + * If we just merged left + cleft and cleft == cright,
> > > + * we no longer have a cright to merge with right. We're done.
> > > + */
> > > + if (cequal)
> > > + return 0;
> > > + }
> > > +
> > > + /* Try to merge cright and right. */
> > > + ulen = (unsigned long long)right.rc_blockcount + cright.rc_blockcount;
> > > + if (right.rc_blockcount != 0 && cright.rc_blockcount != 0 &&
> > > + right.rc_refcount == cright.rc_refcount + adjust &&
> > > + ulen < MAXREFCEXTLEN) {
> > > + trace_xfs_refcount_merge_right_extent(cur->bc_mp,
> > > + cur->bc_private.a.agno, &cright, &right);
> > > + return xfs_refcount_merge_right_extent(cur, &right, &cright,
> > > + agbno, aglen);
> > > + }
> > > +
> > > + return error;
> > > +}
> > > +
> > ...
> > > +/*
> > > + * Adjust the refcounts of middle extents. At this point we should have
> > > + * split extents that crossed the adjustment range; merged with adjacent
> > > + * extents; and updated agbno/aglen to reflect the merges. Therefore,
> > > + * all we have to do is update the extents inside [agbno, agbno + aglen].
> > > + */
> > > +STATIC int
> > > +xfs_refcount_adjust_extents(
> > > + struct xfs_btree_cur *cur,
> > > + xfs_agblock_t agbno,
> > > + xfs_extlen_t aglen,
> > > + xfs_extlen_t *adjusted,
> > > + enum xfs_refc_adjust_op adj,
> > > + struct xfs_defer_ops *dfops,
> > > + struct xfs_owner_info *oinfo)
> > > +{
> > > + struct xfs_refcount_irec ext, tmp;
> > > + int error;
> > > + int found_rec, found_tmp;
> > > + xfs_fsblock_t fsbno;
> > > +
> > > + /* Merging did all the work already. */
> > > + if (aglen == 0)
> > > + return 0;
> > > +
> > > + error = xfs_refcount_lookup_ge(cur, agbno, &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > +
> > > + while (aglen > 0 && xfs_refcount_still_have_space(cur)) {
> > > + error = xfs_refcount_get_rec(cur, &ext, &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + if (!found_rec) {
> > > + ext.rc_startblock = cur->bc_mp->m_sb.sb_agblocks;
> > > + ext.rc_blockcount = 0;
> > > + ext.rc_refcount = 0;
> > > + }
> > > +
> > > + /*
> > > + * Deal with a hole in the refcount tree; if a file maps to
> > > + * these blocks and there's no refcountbt recourd, pretend that
> >
> > Typo: record
>
> Fixed.
>
> > > + * there is one with refcount == 1.
> > > + */
> >
> > Also, what actually confirms that the blocks are file mapped?
>
> There's no explicit check that the (agbno/aglen) range is actually file
> mapped. However, the only way into this function is via the refcount
> deferred ops mechanism, and the only way into that is via
> _refcount_{in,de}crease_extent, which both take xfs_bmbt_irec
> parameters. The only callers of those two functions are
> _reflink_remap_extent and _bmap_del_extent, both of which operate on
> file extents.
>
> So, the only way that unshareable blocks (xattrs, metadata, etc.) can
> end up in the refcount mechanism is malicious code, bugs, or corrupt
> metadata.
>
> > Couldn't blocks absent from the refcbt also reside in the allocbt?
>
> Yes, but if they're in the freespace btrees, they ought not also be
> mapped into a file.
>
> > (I guess the broader question is what are the rules/expectations for
> > handling sparse files..?).
>
> Holes should never get reflinked or bunmapi'd.
>
Ok, thanks for the explanation.
> > > + if (ext.rc_startblock != agbno) {
> > > + tmp.rc_startblock = agbno;
> > > + tmp.rc_blockcount = min(aglen,
> > > + ext.rc_startblock - agbno);
> > > + tmp.rc_refcount = 1 + adj;
> > > + trace_xfs_refcount_modify_extent(cur->bc_mp,
> > > + cur->bc_private.a.agno, &tmp);
> > > +
> > > + /*
> > > + * Either cover the hole (increment) or
> > > + * delete the range (decrement).
> > > + */
> > > + if (tmp.rc_refcount) {
> > > + error = xfs_refcount_insert(cur, &tmp,
> > > + &found_tmp);
> > > + if (error)
> > > + goto out_error;
> > > + XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
> > > + found_tmp == 1, out_error);
> > > + cur->bc_private.a.priv.refc.nr_ops++;
> > > + } else {
> > > + fsbno = XFS_AGB_TO_FSB(cur->bc_mp,
> > > + cur->bc_private.a.agno,
> > > + tmp.rc_startblock);
> > > + xfs_bmap_add_free(cur->bc_mp, dfops, fsbno,
> > > + tmp.rc_blockcount, oinfo);
> > > + }
> > > +
> > > + (*adjusted) += tmp.rc_blockcount;
> > > + agbno += tmp.rc_blockcount;
> > > + aglen -= tmp.rc_blockcount;
> > > +
> > > + error = xfs_refcount_lookup_ge(cur, agbno,
> > > + &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + }
> > > +
> > > + /* Stop if there's nothing left to modify */
> > > + if (aglen == 0 || !xfs_refcount_still_have_space(cur))
> > > + break;
> > > +
> > > + /*
> > > + * Adjust the reference count and either update the tree
> > > + * (incr) or free the blocks (decr).
> > > + */
> > > + if (ext.rc_refcount == MAXREFCOUNT)
> > > + goto skip;
> > > + ext.rc_refcount += adj;
> > > + trace_xfs_refcount_modify_extent(cur->bc_mp,
> > > + cur->bc_private.a.agno, &ext);
> > > + if (ext.rc_refcount > 1) {
> > > + error = xfs_refcount_update(cur, &ext);
> > > + if (error)
> > > + goto out_error;
> > > + cur->bc_private.a.priv.refc.nr_ops++;
> > > + } else if (ext.rc_refcount == 1) {
> > > + error = xfs_refcount_delete(cur, &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > + XFS_WANT_CORRUPTED_GOTO(cur->bc_mp,
> > > + found_rec == 1, out_error);
> > > + cur->bc_private.a.priv.refc.nr_ops++;
> > > + goto advloop;
> > > + } else {
> > > + fsbno = XFS_AGB_TO_FSB(cur->bc_mp,
> > > + cur->bc_private.a.agno,
> > > + ext.rc_startblock);
> > > + xfs_bmap_add_free(cur->bc_mp, dfops, fsbno,
> > > + ext.rc_blockcount, oinfo);
> > > + }
> > > +
> > > +skip:
> > > + error = xfs_btree_increment(cur, 0, &found_rec);
> > > + if (error)
> > > + goto out_error;
> > > +
> > > +advloop:
> > > + (*adjusted) += ext.rc_blockcount;
> > > + agbno += ext.rc_blockcount;
> > > + aglen -= ext.rc_blockcount;
> > > + }
> > > +
> > > + return error;
> > > +out_error:
> > > + trace_xfs_refcount_modify_extent_error(cur->bc_mp,
> > > + cur->bc_private.a.agno, error, _RET_IP_);
> > > + return error;
> > > +}
> > > +
> > > +/* Adjust the reference count of a range of AG blocks. */
> > > +STATIC int
> > > +xfs_refcount_adjust(
> > > + struct xfs_btree_cur *cur,
> > > + xfs_agblock_t agbno,
> > > + xfs_extlen_t aglen,
> > > + xfs_extlen_t *adjusted,
> > > + enum xfs_refc_adjust_op adj,
> > > + struct xfs_defer_ops *dfops,
> > > + struct xfs_owner_info *oinfo)
> > > +{
> > > + xfs_extlen_t orig_aglen;
> > > + bool shape_changed;
> > > + int shape_changes = 0;
> > > + int error;
> > > +
> > > + *adjusted = 0;
> > > + switch (adj) {
> > > + case XFS_REFCOUNT_ADJUST_INCREASE:
> > > + trace_xfs_refcount_increase(cur->bc_mp, cur->bc_private.a.agno,
> > > + agbno, aglen);
> > > + break;
> > > + case XFS_REFCOUNT_ADJUST_DECREASE:
> > > + trace_xfs_refcount_decrease(cur->bc_mp, cur->bc_private.a.agno,
> > > + agbno, aglen);
> > > + break;
> > > + default:
> > > + ASSERT(0);
> > > + }
> > > +
> >
> > Seems like slight overkill... how about a single
> > trace_xfs_refcount_adjust() call that also takes adj as a parameter? We
> > should be able to even print an "inc" or "dec" string or some such if we
> > want for easier filtering.
>
> I prefer to leave the two tracepoints so that I can filter at the
> trace-cmd level:
>
> # trace-cmd record -e xfs_refcount_decrease -F xfs_io...
>
> That said, you're right about the switch being overkill since the enum
> is private to the file. I'll collapse it to an if statement.
>
Sounds fine.
Brian
> Thank you for the review!
>
> --D
>
> >
> > Brian
> >
> > > + /*
> > > + * Ensure that no rcextents cross the boundary of the adjustment range.
> > > + */
> > > + error = xfs_refcount_split_extent(cur, agbno, &shape_changed);
> > > + if (error)
> > > + goto out_error;
> > > + if (shape_changed)
> > > + shape_changes++;
> > > +
> > > + error = xfs_refcount_split_extent(cur, agbno + aglen, &shape_changed);
> > > + if (error)
> > > + goto out_error;
> > > + if (shape_changed)
> > > + shape_changes++;
> > > +
> > > + /*
> > > + * Try to merge with the left or right extents of the range.
> > > + */
> > > + orig_aglen = aglen;
> > > + error = xfs_refcount_merge_extents(cur, &agbno, &aglen, adj,
> > > + &shape_changed);
> > > + if (error)
> > > + goto out_error;
> > > + if (shape_changed)
> > > + shape_changes++;
> > > + (*adjusted) += orig_aglen - aglen;
> > > + if (shape_changes)
> > > + cur->bc_private.a.priv.refc.shape_changes++;
> > > +
> > > + /* Now that we've taken care of the ends, adjust the middle extents */
> > > + error = xfs_refcount_adjust_extents(cur, agbno, aglen, adjusted, adj,
> > > + dfops, oinfo);
> > > + if (error)
> > > + goto out_error;
> > > +
> > > + return 0;
> > > +
> > > +out_error:
> > > + trace_xfs_refcount_adjust_error(cur->bc_mp, cur->bc_private.a.agno,
> > > + error, _RET_IP_);
> > > + return error;
> > > +}
> > > diff --git a/fs/xfs/xfs_error.h b/fs/xfs/xfs_error.h
> > > index 3d22470..d9675c64 100644
> > > --- a/fs/xfs/xfs_error.h
> > > +++ b/fs/xfs/xfs_error.h
> > > @@ -92,7 +92,8 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
> > > #define XFS_ERRTAG_BMAPIFORMAT 21
> > > #define XFS_ERRTAG_FREE_EXTENT 22
> > > #define XFS_ERRTAG_RMAP_FINISH_ONE 23
> > > -#define XFS_ERRTAG_MAX 24
> > > +#define XFS_ERRTAG_REFCOUNT_CONTINUE_UPDATE 24
> > > +#define XFS_ERRTAG_MAX 25
> > >
> > > /*
> > > * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> > > @@ -121,6 +122,7 @@ extern void xfs_verifier_error(struct xfs_buf *bp);
> > > #define XFS_RANDOM_BMAPIFORMAT XFS_RANDOM_DEFAULT
> > > #define XFS_RANDOM_FREE_EXTENT 1
> > > #define XFS_RANDOM_RMAP_FINISH_ONE 1
> > > +#define XFS_RANDOM_REFCOUNT_CONTINUE_UPDATE 1
> > >
> > > #ifdef DEBUG
> > > extern int xfs_error_test_active;
> > >
> > > --
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