[CC += linux-api@] Hello Vlastimil, Since this is a kernel-user-space API change, please CC linux-api@. The kernel source file Documentation/SubmitChecklist notes that all Linux kernel patches that change userspace interfaces should be CCed to linux-api@xxxxxxxxxxxxxxx, so that the various parties who are interested in API changes are informed. For further information, see https://www.kernel.org/doc/man-pages/linux-api-ml.html Cheers, Michael On Thu, Feb 26, 2015 at 2:51 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote: > 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> -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface", http://blog.man7.org/ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
