Just wanted to send out an updated patch set that includes changes (mostly cleanups and fixes) from some of the reviews and discussion at LSF-MM. New changes are: ---------------- o Renamed vrange syscall to mvolatile (Per Hugh's suggestion) o Dropped any modifications made to page age when marking volatile. (from LSF-MM discussion) o Changed "discard" usage to "purged" for clarity/consistency (Kosaki-san's suggestion) o Moved appropriate header definitions to uapi/ (Kosaki-san) o Made sure to take write on mmap_sem (Kosaki-san/Minchan) o Made sure to clean ptes on marking non-volatile rather then cleaning them on fault (Kosaki-san's suggestion) o Introduced a cleanup patch to make adding new psudo-swap types simpler o Numerous other fixes from Minchan o Numerous other fixes suggested by Kosaki-san o For now I've also dropped the naive aging anonymous memory on swapless systems, as I need to sort out accounting details first. Still on the TODO list ---------------------------------------------------- o Look into possibility of doing VMA splitting/merging more carefully by hand to avoid potential allocation failures. This would allow us to go back using madvise() syscall. o Sort out how best to do page accounting when the volatility is tracked on a per-mm basis. o Revisit anonymous page aging on swapless systems o Draft up re-adding tmpfs/shm file volatility support There is of course, the ongoing discussion w/ Johannes about his suggestion of cleaning the pte entries dirty bit to represent volatility. While this method is attractive from a kernel mm-developer point of view, the resulting semantics are quite subtle and I worry would be confusing and error prone for application developers. If consensus builds for that approach, I'm willing to move to that method, but until then I figured I'd continue with this approach, which has simpler semantics (but will require more logic when tmpfs/shm file support is readded). Many thanks again to Minchan, Kosaki-san, Johannes, Jan, Rik, Hugh, and others for the great feedback and discussion at LSF-MM. thanks -john Volatile ranges provides a method for userland to inform the kernel that a range of memory is safe to discard (ie: can be regenerated) but userspace may want to try access it in the future. It can be thought of as similar to MADV_DONTNEED, but that the actual freeing of the memory is delayed and only done under memory pressure, and the user can try to cancel the action and be able to quickly access any unpurged pages. The idea originated from Android's ashmem, but I've since learned that other OSes provide similar functionality. This functionality allows for a number of interesting uses. One such example is: Userland caches that have kernel triggered eviction under memory pressure. This allows for the kernel to "rightsize" userspace caches for current system-wide workload. Things like image bitmap caches, or rendered HTML in a hidden browser tab, where the data is not visible and can be regenerated if needed, are good examples. Both Chrome and Firefox already make use of volatile range-like functionality via the ashmem interface: https://hg.mozilla.org/releases/mozilla-b2g28_v1_3t/rev/a32c32b24a34 https://chromium.googlesource.com/chromium/src/base/+/47617a69b9a57796935e03d78931bd01b4806e70/memory/discardable_memory_allocator_android.cc The basic usage of volatile ranges is as so: 1) Userland marks a range of memory that can be regenerated if necessary as volatile 2) Before accessing the memory again, userland marks the memory as nonvolatile, and the kernel will provide notification if any pages in the range has been purged. If userland accesses memory while it is volatile, it will either get the value stored at that memory if there has been no memory pressure or the application will get a SIGBUS if the page has been purged. Reads or writes to the memory do not affect the volatility state of the pages. You can read more about the history of volatile ranges here (~reverse chronological order): https://lwn.net/Articles/592042/ https://lwn.net/Articles/590991/ http://permalink.gmane.org/gmane.linux.kernel.mm/98848 http://permalink.gmane.org/gmane.linux.kernel.mm/98676 https://lwn.net/Articles/522135/ https://lwn.net/Kernel/Index/#Volatile_ranges Continuing from the last few releases, this revision is reduced in scope when compared to earlier attempts. I've only focused on handled volatility on anonymous memory, and we're storing the volatility in the VMA. This may have performance implications compared with the earlier approach, but it does simplify the approach. I'm open to expanding functionality via flags arguments, but for now I'm wanting to keep focus on what the right default behavior should be and keep the use cases restricted to help get reviewer interest. Additionally, since we don't handle volatility on tmpfs files with this version of the patch, it is not able to be used to implement semantics similar to Android's ashmem. But since shared volatiltiy on files is more complex, my hope is to start small and hopefully grow from there. Again, much of the logic in this patchset is based on Minchan's earlier efforts, so I do want to make sure the credit goes to him for his major contribution! Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Robert Love <rlove@xxxxxxxxxx> Cc: Mel Gorman <mel@xxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Dave Hansen <dave@xxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx> Cc: Neil Brown <neilb@xxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Mike Hommey <mh@xxxxxxxxxxxx> Cc: Taras Glek <tglek@xxxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> Cc: Michel Lespinasse <walken@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Keith Packard <keithp@xxxxxxxxxx> Cc: linux-mm@xxxxxxxxx <linux-mm@xxxxxxxxx> John Stultz (4): swap: Cleanup how special swap file numbers are defined mvolatile: Add mvolatile syscall and handle splitting/merging and marking vmas mvolatile: Add purged page detection on setting memory non-volatile mvolatile: Add page purging logic & SIGBUS trap arch/x86/syscalls/syscall_64.tbl | 1 + include/linux/mm.h | 1 + include/linux/mvolatile.h | 10 + include/linux/swap.h | 36 ++-- include/linux/swapops.h | 10 + include/uapi/linux/mvolatile.h | 7 + mm/Makefile | 2 +- mm/internal.h | 2 - mm/memory.c | 8 + mm/mvolatile.c | 401 +++++++++++++++++++++++++++++++++++++++ mm/rmap.c | 5 + mm/vmscan.c | 12 ++ 12 files changed, 481 insertions(+), 14 deletions(-) create mode 100644 include/linux/mvolatile.h create mode 100644 include/uapi/linux/mvolatile.h create mode 100644 mm/mvolatile.c -- 1.8.3.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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