On Sun, 2011-02-13 at 15:21 -0600, Boyd Stephen Smith Jr. wrote: > In <4d58173b.7050...@gmail.com>, George Shuklin wrote: > >What data stored in Buffers area, and what data a stored in Cached area? > >And what difference between them? > > > >If you know at least one article in kernels sources/Documentation > >folder, or anywhere in Internet, I'll read it gladly. > > http://www.linuxhowtos.org/System/Linux%20Memory%20Management.htm > > First hit when doing this search, here: > http://www.google.com/search?q=what+is+the+difference+between+buffers+and+cache+in+linux+kernel+memory+reports&ie=UTF-8&oe=UTF-8 > > It has a section called "The difference between buffers and cache". > > So, searching the web is a good start but, I can't say I know that there is > specific documentation about this. My understanding is: "cache" is RAM that > exactly mirrors a part of the block device, or at least a whole page in size. > > "cache" is used for satisfying read requests to that part of the block > device, instead of doing real I/O. When a write occurs that that part of the > disk the cache is invalidated and the RAM is scheduled for reuse. "cache" > can be dropped at any time with just a performance hit. "buffers" can be any > size (not necessarily a multiple of the page size) and are used mainly for > write operations. Instead of waiting for I/O to finish before returning from > a system call, data is stored in a "buffer". Once the "buffer" is confirmed > as written to disk, the RAM is scheduled for reuse. "buffers" can't be > dropped until their I/O completes. It seems that buffers can turn into cache > and vice-versa for certain use cases, but I don't know if the kernel actually > does that. > > Both types of memory are effectively free. Cache can be dropped willy-nilly. > > Buffers can be reclaimed by waiting for their I/O to complete. Both of these > actions are done automatically by the kernel when application memory pressure > increases. That's a very helpful description; I never thought of dividing it as read versus write. I do not know the details by any means and this may be a holdover from my long ago CNE days but isn't there much more in buffers than just disk writes, e.g., network I/O is also buffered in memory I Thought. Thanks - John
-- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/1297664724.21905.1.ca...@denise.theartistscloset.com
