Hi Chao, Thanks for the review and suggestions.
I think the below code should work and cover all the cases we discussed. Let me test it and then put up a new patchset for review. Thanks, Sahitya. Mon, Mar 15, 2021 at 06:31:00PM +0800, Chao Yu wrote: > Hi Sahitya, > > On 2021/3/15 17:45, Sahitya Tummala wrote: > >Hi Chao, > > > >On Mon, Mar 15, 2021 at 04:10:22PM +0800, Chao Yu wrote: > >>Hi Sahitya, > >> > >>On 2021/3/15 15:46, Sahitya Tummala wrote: > >>>Hi Chao, > >>> > >>>On Mon, Mar 15, 2021 at 02:12:44PM +0800, Chao Yu wrote: > >>>>Sahitya, > >>>> > >>>>On 2021/3/15 12:56, Sahitya Tummala wrote: > >>>>>When f2fs is heavily utilized over 80%, the current discard policy > >>>>>sets the max sleep timeout of discard thread as 50ms > >>>>>(DEF_MIN_DISCARD_ISSUE_TIME). But this is set even when there are > >>>>>no pending discard commands to be issued. This results into > >>>>>unnecessary frequent and periodic wake ups of the discard thread. > >>>>>This patch adds check for pending discard commands in addition > >>>>>to heavy utilization condition to prevent those wake ups. > >>>> > >>>>Could this commit fix your issue? > >>>> > >>>>https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=43f8c47ea7d59c7b2270835f1d7c4618a1ea27b6 > >>>> > >>>I don't think it will help because we are changing the max timeout of the > >>>dpolicy itself in __init_discard_policy() when util > 80% as below - > >>> > >>>dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME; > >>> > >>>And issue_discard_thread() uses this value as wait_ms, when there > >>>are no more pending discard commands to be issued. > >>><snip> > >>> } else { > >>> wait_ms = dpolicy.max_interval; > >>> } > >>><snip> > >>> > >>>The new patch posted above is not changing anything related to the > >>>max_interval. > >>>Hence, I think it won't help the uncessary wakeup problem I am trying to > >>>solve > >>>for this condition - util > 80% and when there are no pending discards. > >>> > >>>Please let me know if i am missing something. > >> > >>Copied, thanks for the explanation. > >> > >>But there is another case which can cause this issue in the case of > >>disk util < 80%. > >> > >>wait_ms = DEF_MIN_DISCARD_ISSUE_TIME; > >> > >>do { > >> wait_event_interruptible_timeout(, wait_ms); > >> > >> ... > >> > >> if (!atomic_read(&dcc->discard_cmd_cnt)) > >>[1] new statement > >> continue; > >> > >>} while(); > >> > >>Then the loop will wakeup whenever 50ms timeout. > >> > >Yes, only for a short period of time i.e., until the first discard command > >is issued. Once a discard is issued, it will use > >wait_ms = dpolicy.max_interval; > > > >>So, to avoid this case, shouldn't we reset wait_ms to dpolicy.max_interval > >>at [1]? > >> > >Yes, we can add that to cover the above case. > > > >>Meanwhile, how about relocating discard_cmd_cnt check after > >>__init_discard_policy(DPOLICY_FORCE)? and olny set .max_interval to > >>DEF_MAX_DISCARD_ISSUE_TIME if there is no discard command, and keep > >>.granularity to 1? > >> > > > >There is not need to change .granularity, right? It will be controlled > > I think so. > > >as per utilization as it is done today. Only max_interval and wait_ms > >needs to be updated. Does this look good? > > > >diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > >index d7076796..958ad1e 100644 > >--- a/fs/f2fs/segment.c > >+++ b/fs/f2fs/segment.c > >@@ -1772,13 +1772,16 @@ static int issue_discard_thread(void *data) > > wait_ms = dpolicy.max_interval; > > continue; > > } > >- if (!atomic_read(&dcc->discard_cmd_cnt)) > >- continue; > >- > > if (sbi->gc_mode == GC_URGENT_HIGH || > > !f2fs_available_free_memory(sbi, DISCARD_CACHE)) > > __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, > > 1); > > > >+ if (!atomic_read(&dcc->discard_cmd_cnt)) { > >+ dpolicy.max_interval = DEF_MAX_DISCARD_ISSUE_TIME; > >+ wait_ms = dpolicy.max_interval; > >+ continue; > >+ } > > Hmm.. how about cleaning up to configure discard policy in > __init_discard_policy()? > > Something like: > > --- > fs/f2fs/segment.c | 19 ++++++++++++------- > 1 file changed, 12 insertions(+), 7 deletions(-) > > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > index 592927ccffa7..684463a70eb9 100644 > --- a/fs/f2fs/segment.c > +++ b/fs/f2fs/segment.c > @@ -1118,7 +1118,9 @@ static void __init_discard_policy(struct f2fs_sb_info > *sbi, > dpolicy->ordered = true; > if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) { > dpolicy->granularity = 1; > - dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME; > + if (atomic_read(&SM_I(sbi)->dcc_info->discard_cmd_cnt)) > + dpolicy->max_interval = > + DEF_MIN_DISCARD_ISSUE_TIME; > } > } else if (discard_type == DPOLICY_FORCE) { > dpolicy->min_interval = DEF_MIN_DISCARD_ISSUE_TIME; > @@ -1734,8 +1736,15 @@ static int issue_discard_thread(void *data) > set_freezable(); > > do { > - __init_discard_policy(sbi, &dpolicy, DPOLICY_BG, > - dcc->discard_granularity); > + if (sbi->gc_mode == GC_URGENT_HIGH || > + !f2fs_available_free_memory(sbi, DISCARD_CACHE)) > + __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1); > + else > + __init_discard_policy(sbi, &dpolicy, DPOLICY_BG, > + dcc->discard_granularity); > + > + if (!atomic_read(&dcc->discard_cmd_cnt)) > + wait_ms = dpolicy.max_interval; > > wait_event_interruptible_timeout(*q, > kthread_should_stop() || freezing(current) || > @@ -1762,10 +1771,6 @@ static int issue_discard_thread(void *data) > if (!atomic_read(&dcc->discard_cmd_cnt)) > continue; > > - if (sbi->gc_mode == GC_URGENT_HIGH || > - !f2fs_available_free_memory(sbi, DISCARD_CACHE)) > - __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1); > - > sb_start_intwrite(sbi->sb); > > issued = __issue_discard_cmd(sbi, &dpolicy); > -- > 2.29.2 > > Thoughts? > > Thanks, > > >+ > > sb_start_intwrite(sbi->sb); > > > > issued = __issue_discard_cmd(sbi, &dpolicy); > > > >thanks, > >Sahitya. > > > >>Thanks, > >> > >>> > >>>Thanks, > >>>Sahitya. > >>> > >>>>Thanks, > >>>> > >>>>> > >>>>>Signed-off-by: Sahitya Tummala <stumm...@codeaurora.org> > >>>>>--- > >>>>> fs/f2fs/segment.c | 5 ++++- > >>>>> 1 file changed, 4 insertions(+), 1 deletion(-) > >>>>> > >>>>>diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c > >>>>>index dced46c..df30220 100644 > >>>>>--- a/fs/f2fs/segment.c > >>>>>+++ b/fs/f2fs/segment.c > >>>>>@@ -1112,6 +1112,8 @@ static void __init_discard_policy(struct > >>>>>f2fs_sb_info *sbi, > >>>>> struct discard_policy *dpolicy, > >>>>> int discard_type, unsigned int > >>>>> granularity) > >>>>> { > >>>>>+ struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info; > >>>>>+ > >>>>> /* common policy */ > >>>>> dpolicy->type = discard_type; > >>>>> dpolicy->sync = true; > >>>>>@@ -1129,7 +1131,8 @@ static void __init_discard_policy(struct > >>>>>f2fs_sb_info *sbi, > >>>>> dpolicy->io_aware = true; > >>>>> dpolicy->sync = false; > >>>>> dpolicy->ordered = true; > >>>>>- if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) { > >>>>>+ if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL && > >>>>>+ atomic_read(&dcc->discard_cmd_cnt)) { > >>>>> dpolicy->granularity = 1; > >>>>> dpolicy->max_interval = > >>>>> DEF_MIN_DISCARD_ISSUE_TIME; > >>>>> } > >>>>> > >>> > > -- -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
