This series is based on Jerome Marchand's [1] so let me quote the first paragraph from there: There are several shortcomings with the accounting of shared memory (sysV shm, shared anonymous mapping, mapping to a tmpfs file). The values in /proc/<pid>/status and statm don't allow to distinguish between shmem memory and a shared mapping to a regular file, even though theirs implication on memory usage are quite different: at reclaim, file mapping can be dropped or write back on disk while shmem needs a place in swap. As for shmem pages that are swapped-out or in swap cache, they aren't accounted at all. The original motivation for myself is that a customer found (IMHO rightfully) confusing that e.g. top output for process swap usage is unreliable with respect to swapped out shmem pages, which are not accounted for. The fundamental difference between private anonymous and shmem pages is that the latter has PTE's converted to pte_none, and not swapents. As such, they are not accounted to the number of swapents visible e.g. in /proc/pid/status VmSwap row. It might be theoretically possible to use swapents when swapping out shmem (without extra cost, as one has to change all mappers anyway), and on swap in only convert the swapent for the faulting process, leaving swapents in other processes until they also fault (so again no extra cost). But I don't know how many assumptions this would break, and it would be too disruptive change for a relatively small benefit. Instead, my approach is to document the limitation of VmSwap, and provide means to determine the swap usage for shmem areas for those who are interested and willing to pay the price, using /proc/pid/smaps. Because outside of ipcs, I don't think it's possible to currently to determine the usage at all. The previous patchset [1] did introduce new shmem-specific fields into smaps output, and functions to determine the values. I take a simpler approach, noting that smaps output already has a "Swap: X kB" line, where currently X == 0 always for shmem areas. I think we can just consider this a bug and provide the proper value by consulting the radix tree, as e.g. mincore_page() does. In the patch changelog I explain why this is also not perfect (and cannot be without swapents), but still arguably much better than showing a 0. The last two patches are adapted from Jerome's patchset and provide a VmRSS breakdown to VmAnon, VmFile and VmShm in /proc/pid/status. Hugh noted that this is a welcome addition, and I agree that it might help e.g. debugging process memory usage at albeit non-zero, but still rather low cost of extra per-mm counter and some page flag checks. I updated these patches to 4.0-rc1, made them respect !CONFIG_SHMEM so that tiny systems don't pay the cost, and optimized the page flag checking somewhat. [1] http://lwn.net/Articles/611966/ Jerome Marchand (2): mm, shmem: Add shmem resident memory accounting mm, procfs: Display VmAnon, VmFile and VmShm in /proc/pid/status Vlastimil Babka (2): mm, documentation: clarify /proc/pid/status VmSwap limitations mm, proc: account for shmem swap in /proc/pid/smaps Documentation/filesystems/proc.txt | 15 +++++++++++++-- arch/s390/mm/pgtable.c | 5 +---- fs/proc/task_mmu.c | 35 +++++++++++++++++++++++++++++++++-- include/linux/mm.h | 28 ++++++++++++++++++++++++++++ include/linux/mm_types.h | 9 ++++++--- kernel/events/uprobes.c | 2 +- mm/memory.c | 30 ++++++++++-------------------- mm/oom_kill.c | 5 +++-- mm/rmap.c | 15 ++++----------- 9 files changed, 99 insertions(+), 45 deletions(-) -- 2.1.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
