What are the first 2 columns in "top"'s memory report for really? Man page doesn't say!
Hi, on my 4GB RAM machine, top says "Memory: Real: 1293M/3786M act/tot Free: 158M Cache: 2079M Swap: 449M/10G" All the five first columns vary over time, in particular the first four. 3786 + 158 = 3944 is fairly close to 4GB so I guess that's the amount of RAM that the BIOS (+HW drivers?) actually left usable, so that number makes sense. The 158 number is fairly clear also - that's all the RAM that's not in use. And the 2079 number should be the total amount of filesystem cache. But then what are the first two numbers, and there in particular the second one?? I guess the first one is the total amount of malloc():s (I guess including the actual malloc structures). But the second one makes no sense - 1293 (first column) + 2079 (fourth column) make 3372 so this number does not only cover malloc:s and the FS cache then, but there are 414MB of other stuff. Is it that the kernel with all of its work takes 414MB?? If so that's weird because really the machine doesn't do a lot. The "man" page doesn't say any of this. I think it's good to know this, for diagnostic purposes. Anyone knows what the second column is for? Thanks, Tinker
Re: What are the first 2 columns in "top"'s memory report for really? Man page doesn't say!
On Tue, Dec 22, 2015 at 02:31:58AM +0800, Tinker wrote: > Hi, on my 4GB RAM machine, top says > > "Memory: Real: 1293M/3786M act/tot Free: 158M Cache: 2079M Swap: 449M/10G" > > All the five first columns vary over time, in particular the first four. > > 3786 + 158 = 3944 is fairly close to 4GB so I guess that's the amount of RAM > that the BIOS (+HW drivers?) actually left usable, so that number makes > sense. AFAIK: tot: memory allocated by kernel act: memory recently accessed, subset of tot. free: memory not allocated tot + free: total memory available cache: pages allocated to buffer (filesystem) cache all memory includes both kernel and memory used by processes. -Otto > > The 158 number is fairly clear also - that's all the RAM that's not in use. > > And the 2079 number should be the total amount of filesystem cache. > > But then what are the first two numbers, and there in particular the second > one?? > > I guess the first one is the total amount of malloc():s (I guess including > the actual malloc structures). > > But the second one makes no sense - 1293 (first column) + 2079 (fourth > column) make 3372 so this number does not only cover malloc:s and the FS > cache then, but there are 414MB of other stuff. Is it that the kernel with > all of its work takes 414MB?? If so that's weird because really the machine > doesn't do a lot. > > The "man" page doesn't say any of this. > > I think it's good to know this, for diagnostic purposes. > > Anyone knows what the second column is for? > > Thanks, > Tinker
Re: What are the first 2 columns in "top"'s memory report for really? Man page doesn't say!
On 2015-12-22 03:32, Otto Moerbeek wrote: On Tue, Dec 22, 2015 at 02:31:58AM +0800, Tinker wrote: Hi, on my 4GB RAM machine, top says "Memory: Real: 1293M/3786M act/tot Free: 158M Cache: 2079M Swap: 449M/10G" All the five first columns vary over time, in particular the first four. 3786 + 158 = 3944 is fairly close to 4GB so I guess that's the amount of RAM that the BIOS (+HW drivers?) actually left usable, so that number makes sense. AFAIK: tot: memory allocated by kernel act: memory recently accessed, subset of tot. free: memory not allocated tot + free: total memory available cache: pages allocated to buffer (filesystem) cache all memory includes both kernel and memory used by processes. Interesting. Okay so mallocs could be a huge part of the "tot" then. Do you have any idea of the definition of "active" here? (As in what makes a given part of "tot" be declared "active" by the OS.) Also what special treatment may the OS give memory that is not "active", swap it to disk??
Re: What are the first 2 columns in "top"'s memory report for really? Man page doesn't say!
On Tue, Dec 22, 2015 at 04:04:55AM +0800, Tinker wrote: > On 2015-12-22 03:32, Otto Moerbeek wrote: > >On Tue, Dec 22, 2015 at 02:31:58AM +0800, Tinker wrote: > > > >>Hi, on my 4GB RAM machine, top says > >> > >>"Memory: Real: 1293M/3786M act/tot Free: 158M Cache: 2079M Swap: > >>449M/10G" > >> > >>All the five first columns vary over time, in particular the first four. > >> > >>3786 + 158 = 3944 is fairly close to 4GB so I guess that's the amount of > >>RAM > >>that the BIOS (+HW drivers?) actually left usable, so that number makes > >>sense. > > > >AFAIK: > > > >tot: memory allocated by kernel > >act: memory recently accessed, subset of tot. > >free: memory not allocated > >tot + free: total memory available > >cache: pages allocated to buffer (filesystem) cache > > > >all memory includes both kernel and memory used by processes. > > Interesting. > > Okay so mallocs could be a huge part of the "tot" then. > > Do you have any idea of the definition of "active" here? > > (As in what makes a given part of "tot" be declared "active" by the OS.) > > Also what special treatment may the OS give memory that is not "active", > swap it to disk?? > Don't know the details how/when pages are marked inactive, but the general ideas is: inactive r/o pages may be reclaimed when pages are needed, inactive (and dirty) r/w pages may be written to disk (for buffers) or swap (other r/w pages) when pages are needed for other things. -Otto
