On Wed, Sep 18, 2019 at 01:43:11PM -0700, Darrick J. Wong wrote:
> On Mon, Sep 16, 2019 at 08:16:30AM -0400, Brian Foster wrote:
> > The near mode bnobt scan searches left and right in the bnobt
> > looking for the closest free extent to the allocation hint that
> > satisfies minlen. Once such an extent is found, the left/right
> > search terminates, we search one more time in the opposite direction
> > and finish the allocation with the best overall extent.
> >
> > The left/right and find best searches are currently controlled via a
> > combination of cursor state and local variables. Clean up this code
> > and prepare for further improvements to the near mode fallback
> > algorithm by reusing the allocation cursor best extent tracking
> > mechanism. Update the tracking logic to deactivate bnobt cursors
> > when out of allocation range and replace open-coded extent checks to
> > calls to the common helper. In doing so, rename some misnamed local
> > variables in the top-level near mode allocation function.
> >
> > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> > ---
> > fs/xfs/libxfs/xfs_alloc.c | 270 +++++++++++---------------------------
> > fs/xfs/xfs_trace.h | 4 +-
> > 2 files changed, 76 insertions(+), 198 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> > index 2fa7bb6a00a8..edcec975c306 100644
> > --- a/fs/xfs/libxfs/xfs_alloc.c
> > +++ b/fs/xfs/libxfs/xfs_alloc.c
...
> > @@ -1163,96 +1172,44 @@ xfs_alloc_ag_vextent_exact(
> > }
> >
> > /*
> > - * Search the btree in a given direction via the search cursor and compare
> > - * the records found against the good extent we've already found.
> > + * Search the btree in a given direction and check the records against the good
> > + * extent we've already found.
> > */
> > STATIC int
> > xfs_alloc_find_best_extent(
> > - struct xfs_alloc_arg *args, /* allocation argument structure */
> > - struct xfs_btree_cur *gcur, /* good cursor */
> > - struct xfs_btree_cur *scur, /* searching cursor */
> > - xfs_agblock_t gdiff, /* difference for search comparison */
> > - xfs_agblock_t *sbno, /* extent found by search */
> > - xfs_extlen_t *slen, /* extent length */
> > - xfs_agblock_t *sbnoa, /* aligned extent found by search */
> > - xfs_extlen_t *slena, /* aligned extent length */
> > - int dir) /* 0 = search right, 1 = search left */
> > + struct xfs_alloc_arg *args,
> > + struct xfs_alloc_cur *acur,
> > + struct xfs_btree_cur *cur,
> > + bool increment)
> > {
> > - xfs_agblock_t new;
> > - xfs_agblock_t sdiff;
> > int error;
> > int i;
> > - unsigned busy_gen;
> > -
> > - /* The good extent is perfect, no need to search. */
> > - if (!gdiff)
> > - goto out_use_good;
> >
> > /*
> > - * Look until we find a better one, run out of space or run off the end.
> > + * Search so long as the cursor is active or we find a better extent.
> > + * The cursor is deactivated if it extends beyond the range of the
> > + * current allocation candidate.
> > */
> > - do {
> > - error = xfs_alloc_get_rec(scur, sbno, slen, &i);
> > + while (xfs_alloc_cur_active(cur)) {
> > + error = xfs_alloc_cur_check(args, acur, cur, &i);
>
> Does @i > 0 now mean "we found a better candidate for allocation so
> we're done" ?
>
In the context of xfs_alloc_cur_check(), i == 1 just means the checked
extent became the new allocation candidate. Whether "we're done" or not
is a higher level policy decision. In the xfs_alloc_find_best_extent()
case, we're doing a last effort search in the opposite direction after
finding an extent to allocate in the higher level left/right bnobt
search. So yes, we are done in that scenario, but that's not necessarily
the case for all calls to xfs_alloc_cur_check() that return i == 1.
Ideally this could be documented better, but this function is reworked
into xfs_alloc_walk_iter() in the next couple patches and the behavior
changes slightly.
> > if (error)
> > - goto error0;
> > - XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
> > - xfs_alloc_compute_aligned(args, *sbno, *slen,
> > - sbnoa, slena, &busy_gen);
> > -
> > - /*
> > - * The good extent is closer than this one.
> > - */
> > - if (!dir) {
> > - if (*sbnoa > args->max_agbno)
> > - goto out_use_good;
> > - if (*sbnoa >= args->agbno + gdiff)
> > - goto out_use_good;
> > - } else {
> > - if (*sbnoa < args->min_agbno)
> > - goto out_use_good;
> > - if (*sbnoa <= args->agbno - gdiff)
> > - goto out_use_good;
> > - }
> > -
> > - /*
> > - * Same distance, compare length and pick the best.
> > - */
> > - if (*slena >= args->minlen) {
> > - args->len = XFS_EXTLEN_MIN(*slena, args->maxlen);
> > - xfs_alloc_fix_len(args);
> > -
> > - sdiff = xfs_alloc_compute_diff(args->agbno, args->len,
> > - args->alignment,
> > - args->datatype, *sbnoa,
> > - *slena, &new);
> > -
> > - /*
> > - * Choose closer size and invalidate other cursor.
> > - */
> > - if (sdiff < gdiff)
> > - goto out_use_search;
> > - goto out_use_good;
> > - }
> > + return error;
> > + if (i == 1)
> > + break;
> > + if (!xfs_alloc_cur_active(cur))
> > + break;
> >
> > - if (!dir)
> > - error = xfs_btree_increment(scur, 0, &i);
> > + if (increment)
> > + error = xfs_btree_increment(cur, 0, &i);
> > else
> > - error = xfs_btree_decrement(scur, 0, &i);
> > + error = xfs_btree_decrement(cur, 0, &i);
> > if (error)
> > - goto error0;
> > - } while (i);
> > -
> > -out_use_good:
> > - scur->bc_private.a.priv.abt.active = false;
> > - return 0;
> > + return error;
> > + if (i == 0)
> > + cur->bc_private.a.priv.abt.active = false;
>
> ...and I guess @i == 0 here means "@cur hit the end of the records so
> deactivate it"?
>
Yeah, this is a bit of a quirk in that xfs_btree_[inc|dec]rement() are
generic btree functions and so there was no place to bury the 'active'
updates in the first patch of the series. I suppose you could argue that
updating active is a reason to create a couple
xfs_alloc_[inc|dec]rement() wrappers, but I don't have a strong
preference. Thoughts?
> > + }
> >
> > -out_use_search:
> > - gcur->bc_private.a.priv.abt.active = false;
> > return 0;
> > -
> > -error0:
> > - /* caller invalidates cursors */
> > - return error;
> > }
> >
> > /*
> > @@ -1266,23 +1223,13 @@ xfs_alloc_ag_vextent_near(
> > struct xfs_alloc_arg *args)
> > {
> > struct xfs_alloc_cur acur = {0,};
> > - struct xfs_btree_cur *bno_cur;
> > - xfs_agblock_t gtbno; /* start bno of right side entry */
> > - xfs_agblock_t gtbnoa; /* aligned ... */
> > - xfs_extlen_t gtdiff; /* difference to right side entry */
> > - xfs_extlen_t gtlen; /* length of right side entry */
> > - xfs_extlen_t gtlena; /* aligned ... */
> > - xfs_agblock_t gtnew; /* useful start bno of right side */
> > + struct xfs_btree_cur *fbcur = NULL;
> > int error; /* error code */
> > int i; /* result code, temporary */
> > int j; /* result code, temporary */
> > - xfs_agblock_t ltbno; /* start bno of left side entry */
> > - xfs_agblock_t ltbnoa; /* aligned ... */
> > - xfs_extlen_t ltdiff; /* difference to left side entry */
> > - xfs_extlen_t ltlen; /* length of left side entry */
> > - xfs_extlen_t ltlena; /* aligned ... */
> > - xfs_agblock_t ltnew; /* useful start bno of left side */
> > - xfs_extlen_t rlen; /* length of returned extent */
> > + xfs_agblock_t bno;
>
> Is the indenting here inconsistent with the *fbcur declaration above?
>
No, will fix.
> > + xfs_extlen_t len;
> > + bool fbinc = false;
> > #ifdef DEBUG
> > /*
> > * Randomly don't execute the first algorithm.
...
> > @@ -1524,47 +1434,15 @@ xfs_alloc_ag_vextent_near(
> > goto out;
> > }
> >
> > - /*
> > - * At this point we have selected a freespace entry, either to the
> > - * left or to the right. If it's on the right, copy all the
> > - * useful variables to the "left" set so we only have one
> > - * copy of this code.
> > - */
> > - if (xfs_alloc_cur_active(acur.bnogt)) {
> > - bno_cur = acur.bnogt;
> > - ltbno = gtbno;
> > - ltbnoa = gtbnoa;
> > - ltlen = gtlen;
> > - ltlena = gtlena;
> > - j = 1;
> > - } else {
> > - bno_cur = acur.bnolt;
> > - j = 0;
> > - }
> > -
> > - /*
> > - * Fix up the length and compute the useful address.
> > - */
> > - args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
> > - xfs_alloc_fix_len(args);
> > - rlen = args->len;
> > - (void)xfs_alloc_compute_diff(args->agbno, rlen, args->alignment,
> > - args->datatype, ltbnoa, ltlena, <new);
>
> Hmm. So I /think/ the reason this can go away is that
> xfs_alloc_cur_check already did all this trimming and whatnot and
> stuffed the values into the xfs_alloc_cur structure, so we can just copy
> the allocated extent to the caller's @args, update the bnobt/cntbt to
> reflect the allocation, and exit?
>
Right, the code just above should be a subset of what
xfs_alloc_cur_check() is already doing before it selects a new
candidate. This was necessary in the current code because this was all
tracked by cursor state (i.e. xfs_alloc_find_best_extent() decides
whether to use the left or right cursor). This is all replaced with
explicit "best extent" tracking, independent from logic around things
like which direction to do the "find best" search in, etc.
> I think this looks ok, but woof a lot to digest. :/
>
This was the hairiest patch of the set IMO. :P
Brian
> --D
>
> > - ASSERT(ltnew >= ltbno);
> > - ASSERT(ltnew + rlen <= ltbnoa + ltlena);
> > - ASSERT(ltnew + rlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
> > - ASSERT(ltnew >= args->min_agbno && ltnew <= args->max_agbno);
> > - args->agbno = ltnew;
> > -
> > - error = xfs_alloc_fixup_trees(acur.cnt, bno_cur, ltbno, ltlen, ltnew,
> > - rlen, XFSA_FIXUP_BNO_OK);
> > - if (error)
> > - goto out;
> > + args->agbno = acur.bno;
> > + args->len = acur.len;
> > + ASSERT(acur.bno >= acur.rec_bno);
> > + ASSERT(acur.bno + acur.len <= acur.rec_bno + acur.rec_len);
> > + ASSERT(acur.rec_bno + acur.rec_len <=
> > + be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
> >
> > - if (j)
> > - trace_xfs_alloc_near_greater(args);
> > - else
> > - trace_xfs_alloc_near_lesser(args);
> > + error = xfs_alloc_fixup_trees(acur.cnt, acur.bnolt, acur.rec_bno,
> > + acur.rec_len, acur.bno, acur.len, 0);
> >
> > out:
> > xfs_alloc_cur_close(&acur, error);
> > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> > index b12fad3e45cb..2e57dc3d4230 100644
> > --- a/fs/xfs/xfs_trace.h
> > +++ b/fs/xfs/xfs_trace.h
> > @@ -1642,8 +1642,8 @@ DEFINE_ALLOC_EVENT(xfs_alloc_exact_notfound);
> > DEFINE_ALLOC_EVENT(xfs_alloc_exact_error);
> > DEFINE_ALLOC_EVENT(xfs_alloc_near_nominleft);
> > DEFINE_ALLOC_EVENT(xfs_alloc_near_first);
> > -DEFINE_ALLOC_EVENT(xfs_alloc_near_greater);
> > -DEFINE_ALLOC_EVENT(xfs_alloc_near_lesser);
> > +DEFINE_ALLOC_EVENT(xfs_alloc_cur_right);
> > +DEFINE_ALLOC_EVENT(xfs_alloc_cur_left);
> > DEFINE_ALLOC_EVENT(xfs_alloc_near_error);
> > DEFINE_ALLOC_EVENT(xfs_alloc_near_noentry);
> > DEFINE_ALLOC_EVENT(xfs_alloc_near_busy);
> > --
> > 2.20.1
> >
