> I also think that the kernel should commit to either zeroing the page > or leaving it unchanged in response to MADV_FREE (even if the decision > of which to do is made later on). I think that your patch series does > this, but only after a few of the patches are applied (the swap entry > freeing), and I think that it should be a real guaranteed part of the > semantics and maybe have a test case.
This would be a good thing to test because it would be required to add MADV_FREE_UNDO down the road. It would mean the same semantics as the MEM_RESET and MEM_RESET_UNDO features on Windows, and there's probably value in that for the sake of migrating existing software too. For one example, it could be dropped into Firefox: https://dxr.mozilla.org/mozilla-central/source/memory/volatile/VolatileBufferWindows.cpp And in Chromium: https://code.google.com/p/chromium/codesearch#chromium/src/base/memory/discardable_shared_memory.cc Worth noting that both also support the API for pinning/unpinning that's used by Android's ashmem too. Linux really needs a feature like this for caches. Firefox simply doesn't drop the memory at all on Linux right now: https://dxr.mozilla.org/mozilla-central/source/memory/volatile/VolatileBufferFallback.cpp (Lock == pin, Unlock == unpin) For reference: https://msdn.microsoft.com/en-us/library/windows/desktop/aa366887(v=vs.85).aspx
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