| Message ID | 20210802141352.74353-2-paolo.valente@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block, bfq: fix a bug causing a memory leak | expand |
> Il giorno 2 ago 2021, alle ore 16:13, Paolo Valente <paolo.valente@linaro.org> ha scritto: > > The function bfq_setup_merge prepares the merging between two > bfq_queues, say bfqq and new_bfqq. To this goal, it assigns > bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives, > the process that generated that I/O is disassociated from bfqq and > associated with new_bfqq (merging is actually a redirection). In this > respect, bfq_setup_merge increases new_bfqq->ref in advance, adding > the number of processes that are expected to be associated with > new_bfqq. > > Unfortunately, the stable-merging mechanism interferes with this > setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and > before all the expected processes have been associated with > bfqq->new_bfqq, bfqq may happen to be stably merged with a different > queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq > gets changed. So, some of the processes that have been already > accounted for in the ref counter of the previous new_bfqq will not be > associated with that queue. This creates an unbalance, because those > references will never be decremented. > > This commit fixes this issue by reestablishing the previous, natural > behaviour: once bfqq->new_bfqq has been set, it will not be changed > until all expected redirections have occurred. > Hi Jens, did you have time to look at this fix? Thanks, Paolo > Signed-off-by: Davide Zini <davidezini2@gmail.com> > Signed-off-by: Paolo Valente <paolo.valente@linaro.org> > --- > block/bfq-iosched.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index 727955918563..08d9122dd4c0 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -2659,6 +2659,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) > * are likely to increase the throughput. > */ > bfqq->new_bfqq = new_bfqq; > + /* > + * The above assignment schedules the following redirections: > + * each time some I/O for bfqq arrives, the process that > + * generated that I/O is disassociated from bfqq and > + * associated with new_bfqq. Here we increases new_bfqq->ref > + * in advance, adding the number of processes that are > + * expected to be associated with new_bfqq as they happen to > + * issue I/O. > + */ > new_bfqq->ref += process_refs; > return new_bfqq; > } > @@ -2721,6 +2730,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, > { > struct bfq_queue *in_service_bfqq, *new_bfqq; > > + /* if a merge has already been setup, then proceed with that first */ > + if (bfqq->new_bfqq) > + return bfqq->new_bfqq; > + > /* > * Check delayed stable merge for rotational or non-queueing > * devs. For this branch to be executed, bfqq must not be > @@ -2822,9 +2835,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, > if (bfq_too_late_for_merging(bfqq)) > return NULL; > > - if (bfqq->new_bfqq) > - return bfqq->new_bfqq; > - > if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) > return NULL; > > -- > 2.20.1 >
> Il giorno 26 ago 2021, alle ore 11:16, Paolo Valente <paolo.valente@linaro.org> ha scritto: > > > >> Il giorno 2 ago 2021, alle ore 16:13, Paolo Valente <paolo.valente@linaro.org> ha scritto: >> >> The function bfq_setup_merge prepares the merging between two >> bfq_queues, say bfqq and new_bfqq. To this goal, it assigns >> bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives, >> the process that generated that I/O is disassociated from bfqq and >> associated with new_bfqq (merging is actually a redirection). In this >> respect, bfq_setup_merge increases new_bfqq->ref in advance, adding >> the number of processes that are expected to be associated with >> new_bfqq. >> >> Unfortunately, the stable-merging mechanism interferes with this >> setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and >> before all the expected processes have been associated with >> bfqq->new_bfqq, bfqq may happen to be stably merged with a different >> queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq >> gets changed. So, some of the processes that have been already >> accounted for in the ref counter of the previous new_bfqq will not be >> associated with that queue. This creates an unbalance, because those >> references will never be decremented. >> >> This commit fixes this issue by reestablishing the previous, natural >> behaviour: once bfqq->new_bfqq has been set, it will not be changed >> until all expected redirections have occurred. >> > > Hi Jens, > did you have time to look at this fix? > ping ... > Thanks, > Paolo > > >> Signed-off-by: Davide Zini <davidezini2@gmail.com> >> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> >> --- >> block/bfq-iosched.c | 16 +++++++++++++--- >> 1 file changed, 13 insertions(+), 3 deletions(-) >> >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >> index 727955918563..08d9122dd4c0 100644 >> --- a/block/bfq-iosched.c >> +++ b/block/bfq-iosched.c >> @@ -2659,6 +2659,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) >> * are likely to increase the throughput. >> */ >> bfqq->new_bfqq = new_bfqq; >> + /* >> + * The above assignment schedules the following redirections: >> + * each time some I/O for bfqq arrives, the process that >> + * generated that I/O is disassociated from bfqq and >> + * associated with new_bfqq. Here we increases new_bfqq->ref >> + * in advance, adding the number of processes that are >> + * expected to be associated with new_bfqq as they happen to >> + * issue I/O. >> + */ >> new_bfqq->ref += process_refs; >> return new_bfqq; >> } >> @@ -2721,6 +2730,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, >> { >> struct bfq_queue *in_service_bfqq, *new_bfqq; >> >> + /* if a merge has already been setup, then proceed with that first */ >> + if (bfqq->new_bfqq) >> + return bfqq->new_bfqq; >> + >> /* >> * Check delayed stable merge for rotational or non-queueing >> * devs. For this branch to be executed, bfqq must not be >> @@ -2822,9 +2835,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, >> if (bfq_too_late_for_merging(bfqq)) >> return NULL; >> >> - if (bfqq->new_bfqq) >> - return bfqq->new_bfqq; >> - >> if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) >> return NULL; >> >> -- >> 2.20.1
On 8/2/21 8:13 AM, Paolo Valente wrote: > The function bfq_setup_merge prepares the merging between two > bfq_queues, say bfqq and new_bfqq. To this goal, it assigns > bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives, > the process that generated that I/O is disassociated from bfqq and > associated with new_bfqq (merging is actually a redirection). In this > respect, bfq_setup_merge increases new_bfqq->ref in advance, adding > the number of processes that are expected to be associated with > new_bfqq. > > Unfortunately, the stable-merging mechanism interferes with this > setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and > before all the expected processes have been associated with > bfqq->new_bfqq, bfqq may happen to be stably merged with a different > queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq > gets changed. So, some of the processes that have been already > accounted for in the ref counter of the previous new_bfqq will not be > associated with that queue. This creates an unbalance, because those > references will never be decremented. > > This commit fixes this issue by reestablishing the previous, natural > behaviour: once bfqq->new_bfqq has been set, it will not be changed > until all expected redirections have occurred. Applied, thanks.
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 727955918563..08d9122dd4c0 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2659,6 +2659,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) * are likely to increase the throughput. */ bfqq->new_bfqq = new_bfqq; + /* + * The above assignment schedules the following redirections: + * each time some I/O for bfqq arrives, the process that + * generated that I/O is disassociated from bfqq and + * associated with new_bfqq. Here we increases new_bfqq->ref + * in advance, adding the number of processes that are + * expected to be associated with new_bfqq as they happen to + * issue I/O. + */ new_bfqq->ref += process_refs; return new_bfqq; } @@ -2721,6 +2730,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, { struct bfq_queue *in_service_bfqq, *new_bfqq; + /* if a merge has already been setup, then proceed with that first */ + if (bfqq->new_bfqq) + return bfqq->new_bfqq; + /* * Check delayed stable merge for rotational or non-queueing * devs. For this branch to be executed, bfqq must not be @@ -2822,9 +2835,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, if (bfq_too_late_for_merging(bfqq)) return NULL; - if (bfqq->new_bfqq) - return bfqq->new_bfqq; - if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) return NULL;