| Message ID | 20221013224151.300-1-jonathan.derrick@linux.dev (mailing list archive) |
|---|---|
| Headers | show |
| Series | Bitmap percentage flushing | expand |
>>>>> "Jonathan" == Jonathan Derrick <jonathan.derrick@linux.dev> writes: > This introduces a percentage-flushing mechanism that works in-tandem to the > mdadm delay timer. The percentage argument is based on the number of chunks > dirty (rather than percentage), due to large drives requiring smaller and > smaller percentages (eg, 32TB drives-> 1% is 320GB). I've been reading and re-reading this and I still don't understand what you're saying here. You say you're adding a percentage based mechanism, but then you say it's based on chunk counts, not percentages. I think you need to clean this up and re-word it. Maybe you're trying to say that you only take a percentage of the available write bandwidth per second or something like that? > This set hopes to provide a way to make the bitmap flushing more consistent. It > was observed that a synchronous, random write qd1 workload, could make bitmap > writes easily become almost half of the I/O. And in similar workloads with > different timing, it was several minutes between bitmap updates. This is too > inconsistent to be reliable. > This first and second patches adds the flush_threshold parameter. The default > value of 0 defines the default behavior: unplugging immediately just as before. > With a flush-threshold value of 1, it becomes more consistent and paranoid, > flushing on nearly every I/O, leading to a 40% or greater situation. From What situation? Please be more clear here. > there, the flush_threshold can be defined higher for those situations where > power loss is rare and full resync can be tolerated. > The third patch converts the daemon worker to an actual timer. This makes it > more consistent and removes some ugly code. > Jonathan Derrick (3): > md/bitmap: Add chunk-threshold unplugging > md/bitmap: Add sysfs interface for flush threshold > md/bitmap: Convert daemon_work to proper timer > Documentation/admin-guide/md.rst | 5 ++ > drivers/md/md-bitmap.c | 98 +++++++++++++++++++++++++------- > drivers/md/md-bitmap.h | 4 +- > drivers/md/md.c | 9 ++- > drivers/md/md.h | 2 + > 5 files changed, 93 insertions(+), 25 deletions(-) > -- > 2.31.1
On 10/14/2022 3:10 PM, John Stoffel wrote: >>>>>> "Jonathan" == Jonathan Derrick <jonathan.derrick@linux.dev> writes: > >> This introduces a percentage-flushing mechanism that works in-tandem to the >> mdadm delay timer. The percentage argument is based on the number of chunks >> dirty (rather than percentage), due to large drives requiring smaller and >> smaller percentages (eg, 32TB drives-> 1% is 320GB). > > I've been reading and re-reading this and I still don't understand > what you're saying here. You say you're adding a percentage based > mechanism, but then you say it's based on chunk counts, not > percentages. I think you need to clean this up and re-word it.> > Maybe you're trying to say that you only take a percentage of the > available write bandwidth per second or something like that? I'll adjust it to chunk-count-based in the cover letter and make sure it specifies bandwidth. I figured the chunk-count-based was a good way to cover the desired percentage-based feature [1]. [1] https://elixir.bootlin.com/linux/latest/source/drivers/md/md-bitmap.c#L16 > > >> This set hopes to provide a way to make the bitmap flushing more consistent. It >> was observed that a synchronous, random write qd1 workload, could make bitmap >> writes easily become almost half of the I/O. And in similar workloads with >> different timing, it was several minutes between bitmap updates. This is too >> inconsistent to be reliable. > >> This first and second patches adds the flush_threshold parameter. The default >> value of 0 defines the default behavior: unplugging immediately just as before. >> With a flush-threshold value of 1, it becomes more consistent and paranoid, >> flushing on nearly every I/O, leading to a 40% or greater situation. From > > What situation? Please be more clear here. 40% or more of given workload I/Os being bitmap flushes. Will be more clear in v3 > >> there, the flush_threshold can be defined higher for those situations where >> power loss is rare and full resync can be tolerated. > >> The third patch converts the daemon worker to an actual timer. This makes it >> more consistent and removes some ugly code. > >> Jonathan Derrick (3): >> md/bitmap: Add chunk-threshold unplugging >> md/bitmap: Add sysfs interface for flush threshold >> md/bitmap: Convert daemon_work to proper timer > >> Documentation/admin-guide/md.rst | 5 ++ >> drivers/md/md-bitmap.c | 98 +++++++++++++++++++++++++------- >> drivers/md/md-bitmap.h | 4 +- >> drivers/md/md.c | 9 ++- >> drivers/md/md.h | 2 + >> 5 files changed, 93 insertions(+), 25 deletions(-) > >> -- >> 2.31.1 >