> On Aug 27, 2021, at 11:22 PM, Mike Javorski <mike.javorski@xxxxxxxxx> wrote: > > I had some time this evening (and the kernel finally compiled), and > wanted to get this tested. > > The TL;DR: Both patches are needed > > Below are the test results from my replication of Neil's test. It is > readily apparent that both the 5.13.13 kernel AND the 5.13.13 kernel > with the 82011c80b3ec fix exhibit the randomness in read times that > were observed. The 5.13.13 kernel with both the 82011c80b3ec and > f6e70aab9dfe fixes brings the performance back in line with the > 5.12.15 kernel which I tested as a baseline. > > Please forgive the inconsistency in sample counts. This was running as > a while loop, and I just let it go long enough that the behavior was > consistent. Only change to the VM between tests was the different > kernel + a reboot. The testing PC had a consistent workload during the > entire set of tests. > > Test 0: 5.13.10 (base kernel in VM image, just for kicks) > ================================================== > Samples 30 > Min 6.839 > Max 19.998 > Median 9.638 > 75-P 10.898 > 95-P 12.939 > 99-P 18.005 > > Test 1: 5.12.15 (known good) > ================================================== > Samples 152 > Min 1.997 > Max 2.333 > Median 2.171 > 75-P 2.230 > 95-P 2.286 > 99-P 2.312 > > Test 2: 5.13.13 (known bad) > ================================================== > Samples 42 > Min 3.587 > Max 15.803 > Median 6.039 > 75-P 6.452 > 95-P 10.293 > 99-P 15.540 > > Test 3: 5.13.13 + 82011c80b3ec fix > ================================================== > Samples 44 > Min 4.309 > Max 37.040 > Median 6.615 > 75-P 10.224 > 95-P 19.516 > 99-P 36.650 > > Test 4: 5.13.13 + 82011c80b3ec fix + f6e70aab9dfe fix > ================================================== > Samples 131 > Min 2.013 > Max 2.397 > Median 2.169 > 75-P 2.211 > 95-P 2.283 > 99-P 2.348 > > I am going to run the kernel w/ both fixes over the weekend, but > things look good at this point. > > - mike I've targeted Neil's fix for the first 5.15-rc NFSD pull request. I'd like to have Mel's Reviewed-by or Acked-by, though. I will add a Fixes: tag if Neil doesn't repost (no reason to at this point) so the fix should get backported automatically to recent stable kernels. > On Fri, Aug 27, 2021 at 4:49 PM Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote: >> >> >>> On Aug 27, 2021, at 6:00 PM, Mike Javorski <mike.javorski@xxxxxxxxx> wrote: >>> >>> OK, an update. Several hours of spaced out testing sessions and the >>> first patch seems to have resolved the issue. There may be a very tiny >>> bit of lag that still occurs when opening/processing new files, but so >>> far on this kernel I have not had any multi-second freezes. I am still >>> waiting on the kernel with Neil's patch to compile (compiling on this >>> underpowered server so it's taking several hours), but I think the >>> testing there will just be to see if I can show it works still, and >>> then to try and test in a memory constrained VM. To see if I can >>> recreate Neil's experiment. Likely will have to do this over the >>> weekend given the kernel compile delay + fiddling with a VM. >> >> Thanks for your testing! >> >> >>> Chuck: I don't mean to overstep bounds, but is it possible to get that >>> patch pulled into 5.13 stable? That may help things for several people >>> while 5.14 goes through it's shakedown in archlinux prior to release. >> >> The patch had a Fixes: tag, so it should get automatically backported >> to every kernel that has the broken commit. If you don't see it in >> a subsequent 5.13 stable kernel, you are free to ask the stable >> maintainers to consider it. >> >> >>> - mike >>> >>> On Fri, Aug 27, 2021 at 10:07 AM Mike Javorski <mike.javorski@xxxxxxxxx> wrote: >>>> >>>> Chuck: >>>> I just booted a 5.13.13 kernel with your suggested patch. No freezes >>>> on the first test, but that sometimes happens so I will let the server >>>> settle some and try it again later in the day (which also would align >>>> with Neil's comment on memory fragmentation being a contributor). >>>> >>>> Neil: >>>> I have started a compile with the above kernel + your patch to test >>>> next unless you or Chuck determine that it isn't needed, or that I >>>> should test both patches discreetly. As the above is already merged to >>>> 5.14 it seemed logical to just add your patch on top. >>>> >>>> I will also try to set up a vm to test your md5sum scenario with the >>>> various kernels since it's a much faster thing to test. >>>> >>>> - mike >>>> >>>> On Fri, Aug 27, 2021 at 7:13 AM Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote: >>>>> >>>>> >>>>>> On Aug 27, 2021, at 3:14 AM, NeilBrown <neilb@xxxxxxx> wrote: >>>>>> >>>>>> Subject: [PATCH] SUNRPC: don't pause on incomplete allocation >>>>>> >>>>>> alloc_pages_bulk_array() attempts to allocate at least one page based on >>>>>> the provided pages, and then opportunistically allocates more if that >>>>>> can be done without dropping the spinlock. >>>>>> >>>>>> So if it returns fewer than requested, that could just mean that it >>>>>> needed to drop the lock. In that case, try again immediately. >>>>>> >>>>>> Only pause for a time if no progress could be made. >>>>> >>>>> The case I was worried about was "no pages available on the >>>>> pcplist", in which case, alloc_pages_bulk_array() resorts >>>>> to calling __alloc_pages() and returns only one new page. >>>>> >>>>> "No progess" would mean even __alloc_pages() failed. >>>>> >>>>> So this patch would behave essentially like the >>>>> pre-alloc_pages_bulk_array() code: call alloc_page() for >>>>> each empty struct_page in the array without pausing. That >>>>> seems correct to me. >>>>> >>>>> >>>>> I would add >>>>> >>>>> Fixes: f6e70aab9dfe ("SUNRPC: refresh rq_pages using a bulk page allocator") >>>>> >>>>> >>>>>> Signed-off-by: NeilBrown <neilb@xxxxxxx> >>>>>> --- >>>>>> net/sunrpc/svc_xprt.c | 7 +++++-- >>>>>> 1 file changed, 5 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c >>>>>> index d66a8e44a1ae..99268dd95519 100644 >>>>>> --- a/net/sunrpc/svc_xprt.c >>>>>> +++ b/net/sunrpc/svc_xprt.c >>>>>> @@ -662,7 +662,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp) >>>>>> { >>>>>> struct svc_serv *serv = rqstp->rq_server; >>>>>> struct xdr_buf *arg = &rqstp->rq_arg; >>>>>> - unsigned long pages, filled; >>>>>> + unsigned long pages, filled, prev; >>>>>> >>>>>> pages = (serv->sv_max_mesg + 2 * PAGE_SIZE) >> PAGE_SHIFT; >>>>>> if (pages > RPCSVC_MAXPAGES) { >>>>>> @@ -672,11 +672,14 @@ static int svc_alloc_arg(struct svc_rqst *rqstp) >>>>>> pages = RPCSVC_MAXPAGES; >>>>>> } >>>>>> >>>>>> - for (;;) { >>>>>> + for (prev = 0;; prev = filled) { >>>>>> filled = alloc_pages_bulk_array(GFP_KERNEL, pages, >>>>>> rqstp->rq_pages); >>>>>> if (filled == pages) >>>>>> break; >>>>>> + if (filled > prev) >>>>>> + /* Made progress, don't sleep yet */ >>>>>> + continue; >>>>>> >>>>>> set_current_state(TASK_INTERRUPTIBLE); >>>>>> if (signalled() || kthread_should_stop()) { >>>>> >>>>> -- >>>>> Chuck Lever >>>>> >>>>> >>>>> >> >> -- >> Chuck Lever >> >> >> -- Chuck Lever