Insufficient memory for hibernation with kernel 6.17

[acarstoiu]

I believe it started after upgrading the gentoo-sources kernel from 6.17.6 to 6.17.7, but I'm sure it worked just fine with 6.16.12. In any case, before posting a bug on the kernel's Bugzilla, I want to check with you for possible explanations other than a bug.
Whether I try to hibernate by running

Code: Select all

echo disk > /sys/power/state

or by using the KDE Plasma menu (with elogind underneath), the result is just the same:

# dmesg | fgrep -C 2 "Not enough free"
[ 115.425467] PM: hibernation: Creating image:
[ 115.605272] PM: hibernation: Need to copy 1034086 pages
[ 115.605277] PM: hibernation: Not enough free memory
[ 115.425998] PM: hibernation: Error -12 creating image
[ 115.426009] ACPI: PM: Restoring platform NVS memory
--
[12969.416937] PM: hibernation: Creating image:
[12969.603243] PM: hibernation: Need to copy 1173639 pages
[12969.603248] PM: hibernation: Not enough free memory
[12969.417467] PM: hibernation: Error -12 creating image
[12969.417477] ACPI: PM: Restoring platform NVS memory
--
[15435.266025] PM: hibernation: Creating image:
[15435.268343] PM: hibernation: Need to copy 1135535 pages
[15435.268343] PM: hibernation: Not enough free memory
[15435.268343] PM: hibernation: Error -12 creating image
[15435.268343] ACPI: PM: Restoring platform NVS memory
--
[19313.907975] PM: hibernation: Creating image:
[19313.911060] PM: hibernation: Need to copy 1035412 pages
[19313.911060] PM: hibernation: Not enough free memory
[19313.911060] PM: hibernation: Error -12 creating image
[19313.911060] ACPI: PM: Restoring platform NVS memory
--
[22946.540965] PM: hibernation: Creating image:
[22946.543076] PM: hibernation: Need to copy 1046173 pages
[22946.543076] PM: hibernation: Not enough free memory
[22946.543076] PM: hibernation: Error -12 creating image
[22946.543076] ACPI: PM: Restoring platform NVS memory

# LANG=en_US.UTF-8 free -k
total used free shared buff/cache available
Mem: 7553808 3921892 3210932 733844 1165792 3631916
Swap: 16777212 7347720 9429492

The page size is 4KiB, as implied by dmesg messages such as

[15427.731732] PM: hibernation: Allocated 747345 pages for snapshot
[15427.731737] PM: hibernation: Allocated 2989380 kbytes in 6.70 seconds (446.17 MB/s)

and by /proc/1/smaps.
The question is why doesn't the kernel find enough room for those 4 GiB of image in the swap space as the available swap is more than the double of that quantity?

I also tried hibernating after changing /sys/power/image_size to 0 from the default 2/5 of physical memory size. It worked, because the image size way smaller this time:

[25074.727908] PM: hibernation: Creating image:
[25074.731043] PM: hibernation: Need to copy 562810 pages

Mind that the memory load of the machine was not changed during the last two attempts, as much as humanly possible.

[acarstoiu]

In case someone brings into discussion the quote from https://www.kernel.org/doc/Documentation/power/pci.rst

The freezing of devices is carried out after enough memory has been freed (at
the time of this writing the image creation requires at least 50% of system RAM
to be free) in the following three phases:

prepare, freeze, freeze_noirq

I answer this: there's enough room in swap to evict some pages from RAM in order to obtain the 50% free and still remains plenty of space for the hibernation image. Anyway, that vague statement from the said document is no explanation here, as hibernation works with a smaller image (probably obtained with a higher compression factor).