On 08/05/2015 03:01 PM, Vlastimil Babka wrote: > Reposting due to lack of feedback in May. I hope at least patches 1 and 2 > could be merged as they are IMHO bugfixes. 3 and 4 is optional but IMHO useful. > > Changes since v2: > o Rebase on next-20150805. > o This means that /proc/pid/maps has the proportional swap share (SwapPss:) > field as per https://lkml.org/lkml/2015/6/15/274 > It's not clear what to do with shmem here so it's 0 for now. > - swapped out shmem doesn't have swap entries, so we would have to look at who > else has the shmem object (partially) mapped > - to be more precise we should also check if his range actually includes > the offset in question, which could get rather involved > - or is there some easy way I don't see? Hmm... This is much more difficult than I envision when commenting on Minchan patch. One possibility could be to have the pte of paged out shmem pages set in a similar way than regular swap entry are. But that would need to use some very precious estate on the pte. As it is, a zero value, while obviously wrong, has the advantage of not being misleading like a bad approximation would be (like the kind which doesn't properly accounts for partial mapping). Jerome > o Konstantin suggested for patch 3/4 that I drop the CONFIG_SHMEM #ifdefs > I didn't see the point in going against tinyfication when the work is > already done, but I can do that if more people think it's better and it > would block the series. > > Changes since v1: > o In Patch 2, rely on SHMEM_I(inode)->swapped if possible, and fallback to > radix tree iterator on partially mapped shmem objects, i.e. decouple shmem > swap usage determination from the page walk, for performance reasons. > Thanks to Jerome and Konstantin for the tips. > The downside is that mm/shmem.c had to be touched. > > 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 | 18 ++++++++++--- > arch/s390/mm/pgtable.c | 5 +--- > fs/proc/task_mmu.c | 52 ++++++++++++++++++++++++++++++++++-- > include/linux/mm.h | 28 ++++++++++++++++++++ > include/linux/mm_types.h | 9 ++++--- > include/linux/shmem_fs.h | 6 +++++ > kernel/events/uprobes.c | 2 +- > mm/memory.c | 30 +++++++-------------- > mm/oom_kill.c | 5 ++-- > mm/rmap.c | 15 +++-------- > mm/shmem.c | 54 ++++++++++++++++++++++++++++++++++++++ > 11 files changed, 178 insertions(+), 46 deletions(-) >
Attachment:
signature.asc
Description: OpenPGP digital signature