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The changes tracking made developers implement [[Memory images deduplication]] for shmem segments as well.
The changes tracking made developers implement [[Memory images deduplication]] for shmem segments as well.
===
== Dumping present pages ==
When dumping the contents of shared memory CRIU doesn't dump all the data. Instead, it determines which pages contain
it and dumps only them. This is done similarly to how regular [[memory dumping and restoring]] works, i.e. by analyzing
the owners' pagemap entries for PRESENT or SWAPPED bits. But there's one feature of shmem dumps -- sometimes shmem
page can exist in the kernel, but not mapped to any process. In this case criu detects one by calling mincore() on
the shmem segment, which reports back the page in-memory status. And the mincore bitmap is AND-ed with the per-process
ones.
== See also ==
[[Memory dumping and restoring]]
[[Memory images deduplication]]
[[Category:Memory]]
[[Category:Memory]]
[[Category:Under the hood]]
[[Category:Under the hood]]