Zero-ing pages when freed

Hi,

I'm working on migrating a virtual machine running Linux, from one host to another, sending the memory via network. Since the hosts are connected via the internet, the connection is somewhat limited, so I compress the memory before sending it, to minimize it.

I'd like to make the conditions for compression better, so I'd like to zero-ing pages when freed, but after reading through mm/page_alloc.c I'm not sure how to do it, so I'd appreciate it if someone could give me a few pointers

Just as a follow up...
After talking to Peter Zijlstra in the kernelnewbies IRC channel, I tried inserting a call to prep_zero_page() in __free_one_page(), which actually got the job done, and compression of the saved memory improved a great deal! Unfortunately the performance penalty for a program which allocates and deallocates a lot is quite high, so it is unlikely that this approach is actually useful...

since the page is already free, why do we need to compress it? how about intelligently compressing only those still in use, and then decompress and restore back only all these during migration.....zeroing is not really needed.....

Quote:

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since the page is already free, why do we need to compress it? how about intelligently compressing only those still in use, and then decompress and restore back only all these during migration.....zeroing is not really needed.....

When using para virtualization you might be right, but when using full virtualization that approach is not possible.