On Thu, Mar 12, 2015 at 11:35:13AM -0400, Michal Hocko wrote: > > > On Wed 11-03-15 19:10:44, Marcos Dione wrote: > [...] > > > > $ free > > > > total used free shared buffers cached > > > > Mem: 396895176 395956332 938844 0 8972 356409952 > > > > -/+ buffers/cache: 39537408 357357768 > > > > Swap: 8385788 8385788 0 > > > > > > > > This reports 378GiB of RAM, 377 used; of those 8MiB in buffers, > > > > 339GiB in cache, leaving only 38Gib for processes (for some reason this > > > > > > I am not sure I understand your math here. 339G in the cache should be > > > reclaimable (be careful about the shmem though). It is the rest which > > > might be harder to reclaim. > > > > These 38GiB I mention is the rest of 378 available minus 339 in > > cache. To me this difference represents the sum of the resident > > anonymous memory malloc'ed by all processes. Unless there's some othr > > kind of pages accounted in 'Used'. > > The kernel needs memory as well for its internal data structures > (stacks, page tables, slab objects, memory used by drivers and what not). Are those in or out of the total memory reported by free? I had the impression the were out. 396895176 accounts only for 378.5GiB of the 384 available in the machine; I assumed the missing 5.5 was kernel memory. > > Yes, but my question was more on the lines of 'why free or > > /proc/meminfo do not show it'. Maybe it's just that it's difficult to > > define (like I said, "sum of resident anonymous..." &c) or nobody really > > cares about this. Maybe I shouldn't either. > > meminfo is exporting this information as AnonPages. I think that what I'm trying to do is figure out what each value represents and where it's incuded, as if to make a graph like this (fields in /proc/meminfo between []'s; dots are inactive, plus signs active): RAM swap other (mmaps) |------------------------------|-----------------------------|-------------... |.| kernel [Slab+KernelStack+PageTables+?] |.| buffers [Buffers] | . . . . .. .| swap cached (not necesarily like this, but you get the idea) (I'm assuming that it only includes anon pages, shms and private mmaps) [SwapCached] |++..| resident annon (malloc'ed) [AnonPages/Active/Inactive(anon)] |+++....+++........| cache [Cached/Active/Inactive(file)] |+++...| (resident?) shms [Shmem] |+++..| resident mmaps |.....| other fs cache |..| free [MemFree] |.............| used swap [SwapTotal-SwapFree] |...............| swap free [SwapFree] Note that there are no details on how the swap is used between anon pages, shm and others; neither about mmaps; except in /proc/<pid>/smaps. If someone is really interested in that, it would have to poll an interesting amount of files, but definitely doable. Just cat'ing one of these files for a process with 128 mmaps and 1 shm as before gave these times: real 0m0.802s user 0m0.004s sys 0m0.244s > > I understand what /proc/sys/vm/overcommit_memory is for; what I > > don't understand is what exactly counted in the Committed_AS line in > > /proc/meminfo. > > It accounts all the address space reservations - e.g. mmap(len), len > will get added. The things are slightly more complicated but start > looking at callers of security_vm_enough_memory_mm should give you an > idea what everything is included. > How is this number used depends on the overcommit mode. > __vm_enough_memory would give you a better picture. > > > I also read Documentation/vm/overcommit-accounting > > What would help you to understand it better? I think that after this dip in terminology I should go back to it and try again to figure it out myself :) Of course findings will be posted. Cheers, -- Marcos. -- 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>