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bcachefs: Eliminate memory barrier from fast path of journal_preres_put()

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Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2021-04-03 21:31:02 -04:00 committed by Kent Overstreet
parent 08e337618f
commit 671cc8a51b
3 changed files with 25 additions and 19 deletions
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2
fs/bcachefs/journal.c
View file

@ -520,7 +520,7 @@ static bool journal_preres_available(struct journal *j,
unsigned new_u64s,
unsigned flags)
{
bool ret = bch2_journal_preres_get_fast(j, res, new_u64s, flags);
bool ret = bch2_journal_preres_get_fast(j, res, new_u64s, flags, true);
if (!ret && mutex_trylock(&j->reclaim_lock)) {
bch2_journal_reclaim(j);

37
fs/bcachefs/journal.h
View file

@ -411,7 +411,12 @@ static inline void bch2_journal_preres_put(struct journal *j,
s.v = atomic64_sub_return(s.v, &j->prereserved.counter);
res->u64s = 0;
closure_wake_up(&j->preres_wait);
if (unlikely(s.waiting)) {
clear_bit(ilog2((((union journal_preres_state) { .waiting = 1 }).v)),
(unsigned long *) &j->prereserved.v);
closure_wake_up(&j->preres_wait);
}
if (s.reserved <= s.remaining &&
!test_bit(JOURNAL_MAY_GET_UNRESERVED, &j->flags)) {
@ -427,32 +432,32 @@ int __bch2_journal_preres_get(struct journal *,
static inline int bch2_journal_preres_get_fast(struct journal *j,
struct journal_preres *res,
unsigned new_u64s,
unsigned flags)
unsigned flags,
bool set_waiting)
{
int d = new_u64s - res->u64s;
union journal_preres_state old, new;
u64 v = atomic64_read(&j->prereserved.counter);
int ret;
do {
old.v = new.v = v;
ret = 0;
new.reserved += d;
/*
* If we're being called from the journal reclaim path, we have
* to unconditionally give out the pre-reservation, there's
* nothing else sensible we can do - otherwise we'd recurse back
* into the reclaim path and deadlock:
*/
if (!(flags & JOURNAL_RES_GET_RESERVED) &&
new.reserved > new.remaining)
if ((flags & JOURNAL_RES_GET_RESERVED) ||
new.reserved + d < new.remaining) {
new.reserved += d;
ret = 1;
} else if (set_waiting && !new.waiting)
new.waiting = true;
else
return 0;
} while ((v = atomic64_cmpxchg(&j->prereserved.counter,
old.v, new.v)) != old.v);
res->u64s += d;
return 1;
if (ret)
res->u64s += d;
return ret;
}
static inline int bch2_journal_preres_get(struct journal *j,
@ -463,7 +468,7 @@ static inline int bch2_journal_preres_get(struct journal *j,
if (new_u64s <= res->u64s)
return 0;
if (bch2_journal_preres_get_fast(j, res, new_u64s, flags))
if (bch2_journal_preres_get_fast(j, res, new_u64s, flags, false))
return 0;
if (flags & JOURNAL_RES_GET_NONBLOCK)

5
fs/bcachefs/journal_types.h
View file

@ -105,8 +105,9 @@ union journal_preres_state {
};
struct {
u32 reserved;
u32 remaining;
u64 waiting:1,
reserved:31,
remaining:32;
};
};