I recently got a chance to try to implement Johannes' suggested approach so I wanted to send it out for comments. It looks like Minchan has also done the same, but from a different direction, focusing on the MADV_FREE use cases. I think both approaches are valid, so I wouldn't consider these patches to be in conflict. Its just that earlier iterations of the volatile range patches had tried to handle numerous different use cases, and the resulting complexity was apparently making it difficult to review and get interest in the patch set. So basically we're splitting the use cases up and trying to find simpler solutions for each. I'd greatly appreciate any feedback or thoughts! 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: * 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. * Opportunistic freeing of memory that may be quickly reused. Minchan has done a malloc implementation where free() marks the pages as volatile, allowing the kernel to reclaim under pressure. This avoids the unmapping and remapping of anonymous pages on free/malloc. So if userland wants to malloc memory quickly after the free, it just needs to mark the pages as non-volatile, and only purged pages will have to be faulted back in. There are two basic ways this can be used: Explicit marking method: 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. Optimistic method: 1) Userland marks a large range of data as volatile 2) Userland continues to access the data as it needs. 3) If userland accesses a page that has been purged, the kernel will send a SIGBUS 4) Userspace can trap the SIGBUS, mark the affected pages as non-volatile, and refill the data as needed before continuing on You can read more about the history of volatile ranges here: 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 This version of the patchset, at Johannes Weiner's suggestion, is much reduced in scope compared to earlier attempts. I've only 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. Further, the page discarding happens via normal vmscanning, which due to anonymous pages not being aged on swapless systems, means we'll only purge pages when swap is enabled. I'll be looking at enabling anonymous aging when swap is disabled to resolve this, but I wanted to get this out for initial comment. 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. Also, much of the logic in this patchset is based on Minchan's earlier efforts. On this iteration, I've not been in close collaboration with him, so I don't want to mis-attribute my rework of the code as his design, but 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: Dhaval Giani <dgiani@xxxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> Cc: Michel Lespinasse <walken@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: linux-mm@xxxxxxxxx <linux-mm@xxxxxxxxx> John Stultz (3): vrange: Add vrange syscall and handle splitting/merging and marking vmas vrange: Add purged page detection on setting memory non-volatile vrange: Add page purging logic & SIGBUS trap arch/x86/syscalls/syscall_64.tbl | 1 + include/linux/mm.h | 1 + include/linux/swap.h | 15 +- include/linux/vrange.h | 22 +++ mm/Makefile | 2 +- mm/internal.h | 2 - mm/memory.c | 21 +++ mm/rmap.c | 5 + mm/vmscan.c | 12 ++ mm/vrange.c | 306 +++++++++++++++++++++++++++++++++++++++ 10 files changed, 382 insertions(+), 5 deletions(-) create mode 100644 include/linux/vrange.h create mode 100644 mm/vrange.c -- 1.8.3.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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