different speed ssd partitions

I have Samsung NVMe SSD 960EVO 250GB disk and it gives me some weird result when testing read speed using hdparm -tT.

Speeds before trim

/dev/nvme0n1:
 Timing cached reads:   24486 MB in  2.00 seconds = 12256.70 MB/sec
 Timing buffered disk reads: 5502 MB in  3.00 seconds = 1832.95 MB/sec
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p1

/dev/nvme0n1p1:
 Timing cached reads:   24878 MB in  2.00 seconds = 12452.22 MB/sec
 Timing buffered disk reads: 190 MB in  0.09 seconds = 2151.12 MB/sec
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p2

/dev/nvme0n1p2:
 Timing cached reads:   24270 MB in  2.00 seconds = 12147.96 MB/sec
 Timing buffered disk reads: 5308 MB in  3.00 seconds = 1769.32 MB/sec
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p3

/dev/nvme0n1p3:
 Timing cached reads:   22976 MB in  2.00 seconds = 11499.27 MB/sec
 Timing buffered disk reads: 7140 MB in  3.00 seconds = 2379.80 MB/sec
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p4

/dev/nvme0n1p4:
 Timing cached reads:   23908 MB in  2.00 seconds = 11967.15 MB/sec
 Timing buffered disk reads: 7022 MB in  3.00 seconds = 2339.82 MB/sec

Speeds after trim

jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1

/dev/nvme0n1:
 Timing cached reads:   25168 MB in  2.00 seconds = 12597.67 MB/sec                                                                                                                                               
 Timing buffered disk reads: 5548 MB in  3.00 seconds = 1848.97 MB/sec                                                                                                                                            
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p1

/dev/nvme0n1p1:                                                                                                                                                                                                   
 Timing cached reads:   25226 MB in  2.00 seconds = 12627.85 MB/sec                                                                                                                                               
 Timing buffered disk reads: 190 MB in  0.09 seconds = 2177.97 MB/sec                                                                                                                                             
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p2

/dev/nvme0n1p2:                                                                                                                                                                                                   
 Timing cached reads:   24356 MB in  2.00 seconds = 12191.47 MB/sec                                                                                                                                               
 Timing buffered disk reads: 5424 MB in  3.00 seconds = 1807.88 MB/sec                                                                                                                                            
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p3

/dev/nvme0n1p3:
 Timing cached reads:   24770 MB in  2.00 seconds = 12398.57 MB/sec
 Timing buffered disk reads: 7590 MB in  3.00 seconds = 2529.50 MB/sec
jkalmar@supercomp:~> sudo hdparm -tT /dev/nvme0n1p4

/dev/nvme0n1p4:
 Timing cached reads:   24532 MB in  2.00 seconds = 12279.30 MB/sec
 Timing buffered disk reads: 6960 MB in  3.00 seconds = 2319.36 MB/sec

You can see that the trim helped except for last partition which is actually slower, but the speed is rather good. What is not good is the speed of second partition.

mount options:

/dev/nvme0n1p1 on /boot/efi type vfat (rw,relatime,fmask=0002,dmask=0002,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro)
/dev/nvme0n1p2 on / type ext4 (rw,relatime,data=ordered)
/dev/nvme0n1p3 on /home type ext4 (rw,relatime,data=ordered)
/dev/nvme0n1p4 on /zaloha type ext4 (rw,relatime,data=ordered)

df -h

Filesystem      Size  Used Avail Use% Mounted on
/dev/nvme0n1p2   23G  8,1G   14G  38% /
/dev/nvme0n1p1  188M  4,6M  183M   3% /boot/efi
/dev/nvme0n1p3  110G   27G   82G  25% /home
/dev/nvme0n1p4   82G   16G   65G  20% /zaloha

smart data

=== START OF SMART DATA SECTION ===
SMART/Health Information (NVMe Log 0x02, NSID 0xffffffff)
Critical Warning:                   0x00
Temperature:                        34 Celsius
Available Spare:                    100%
Available Spare Threshold:          10%
Percentage Used:                    0%
Data Units Read:                    1 168 294 [598 GB]
Data Units Written:                 470 952 [241 GB]
Host Read Commands:                 6 529 515
Host Write Commands:                4 815 912
Controller Busy Time:               22
Power Cycles:                       63
Power On Hours:                     59
Unsafe Shutdowns:                   9
Media and Data Integrity Errors:    0
Error Information Log Entries:      0
Warning  Comp. Temperature Time:    0
Critical Comp. Temperature Time:    0
Temperature Sensor 1:               34 Celsius
Temperature Sensor 2:               35 Celsius

You can see that the drive is quite new according to smart data.

parted

(parted) print                                                           
Model: NVMe Device (nvme)
Disk /dev/nvme0n1: 488397168s
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start       End         Size        File system  Name  Flags
 1      2048s       391167s     389120s     fat32              boot, esp
 2      391168s     49219583s   48828416s   ext4
 3      49219584s   283594751s  234375168s  ext4
 4      283594752s  457674751s  174080000s  ext4

(parted) align-check optimal 1                                            
1 aligned
(parted) align-check optimal 2
2 aligned
(parted) align-check optimal 3
3 aligned
(parted) align-check optimal 4
4 aligned

Everything looks good, but the speed of partition 2 is way slower that the rest. Does anybody know why and how to fix it if it can be fixed?