Hi Andrew and people reading those lists, I still struggle to understand what is wrong with me. I rebuilt my mdadm + bcache array to be sure it was not something linked to a (too) old configuration. Upgrading to 6.16.10 didn't change anything. One symptom of the problem I identified is the time of the swapoff command (I have 32G, 12G are free and there is less than 1G in the swap) MiB Mem : 31952,0 total, 12646,2 free,  2226,8 used, 17587,5 buff/cache MiB Swap: 36000,0 total, 35212,2 free,   787,8 used. 29725,2 avail Mem *$ time sudo swapoff -a * * real6m41,276s user0m0,005s sys0m0,028s* Waiting for more than  6 minutes elapsed for 33 ms of work is bizarre. During that time, if I try to launch another tab with *iotop*, nothing is displayed during at least one minute. During that time, my computer is almost idle. So it looks like swapoff and iotop are stucked, waiting for some kind of a semaphore inside the kernel. Any idea  to dig further ? Thanks, Pierre Le 30/09/2025 à 01:07, Andrew Morton a écrit : > (switched to email. Please respond via emailed reply-to-all, not via the > bugzilla web interface). > > On Sat, 27 Sep 2025 08:07:59 +0000bugzilla-daemon@kernel.org wrote: > >> https://bugzilla.kernel.org/show_bug.cgi?id=220605 >> >> Bug ID: 220605 >> Summary: Very slow access on HDD when a swap partition is used >> on this HDD on kernel 6.16 >> Product: Memory Management >> Version: 2.5 >> Hardware: Intel >> OS: Linux >> Status: NEW >> Severity: high >> Priority: P3 >> Component: Page Allocator >> Assignee:akpm@linux-foundation.org >> Reporter:pierre.juhen@orange.fr >> Regression: No >> >> Hello everybody, >> >> I have a strange behavior on my system (Fedora 42 up to date => kernel 6.16.8). > You certainly do. I wonder what we did to cause this. > > I'll cc the MM development list. Please prefer to report issues over > email this way - we don't use bugzilla and it's rather annoying that MM > bugzilla even exists. > > >> I have many disks but but my two swap partitions are on 2 HDD, sda and sdb, >> which are identical (SEAGATE Barracuda 2To). Swap partition on sda has a higher >> priority than the one on sdb. >> >> I don't use zram. >> >> When a swap partion is used, the disk on wich it seats is very slow. >> >> $ sudo hdparm -t /dev/sda >> /dev/sda: >> Timing buffered disk reads: 24 MB in 3.72 seconds = 6.46 MB/sec >> >> $ sudo hdparm -t /dev/sdb >> /dev/sdb: >> Timing buffered disk reads: 540 MB in 3.16 seconds = 170.85 MB/sec >> pierre@pierre:~$ >> >> Sometimes, speed gets down to less than 2 MB/s. >> >> Lets turn swap off => swapoff -a >> >> $ sudo hdparm -t /dev/sdb >> /dev/sdb: >> Timing buffered disk reads: 462 MB in 3.00 seconds = 153.75 MB/sec >> >> $ sudo hdparm -t /dev/sda >> >> /dev/sda: >> Timing buffered disk reads: 474 MB in 3.00 seconds = 157.84 MB/sec >> pierre@pierre:~$ >> >> Now speed is normal. >> >> Lets put swap on again => sudo swapon -a >> >> Speed is still normal : >> >> $ sudo hdparm -t /dev/sda >> /dev/sda: >> Timing buffered disk reads: 612 MB in 3.01 seconds = 203.56 MB/sec >> $ sudo hdparm -t /dev/sdb >> /dev/sdb: >> Timing buffered disk reads: 570 MB in 3.00 seconds = 189.95 MB/sec >> pierre@pierre:~$ >> >> But swap is not used >> >> MiB Mem : 31952,0 total, 27091,7 free, 3057,6 used, 2343,0 buff/cache >> MiB Swap: 36000,0 total, 36000,0 free, 0,0 used. 28894,4 avail Mem >> >> >> So I suspect that, when the swap is used, there is some sort of lock that slows >> the whole disk that contains the swap partition that is being used. >> >> Logically, the system becomes very slow. >> >> There is nothing in the journal that seems related to this problem. >> >> Since the virtual memory has been modified in 6.16, I suspect a nasty bug. >> >> This affects 6.16.5 to 6.16.8. >> >> This appeared "recently", probably with 6.16 >> >> Thanks, >> >> Regards, >> >> Pierre >> >> -- >> You may reply to this email to add a comment. >> >> You are receiving this mail because: >> You are the assignee for the bug.