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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]]