On 2013-02-16, at 21:04, Subranshu Patel <spatel.ml@xxxxxxxxx> wrote: > I created 2 filesystem on my system (RHEL 6.3, kernel version 2.6.32) > - XFS and EXT4 and mounted them. > > On both the filesystem I executed the mdtest tool(opensource tool) for > 64 concurrent process. Each process performed the following: > - Create large number of directories > - Remove all the directories > > During this time I monitored the memory usage of the system using sar > command. I checked the 3 components - kbmemused, kbbuffers and > kbcached > > kbmemused - Amount of used memory in kilobytes. This does not take > into account memory used by the kernel itself. > kbbuffers - buffer cache > kbcached - page cache > > While the kbmemused and kbcached component was almost similar in EXT4 > and XFS (XFS being a little higher), the kbbuffer showed a totally > different trend. > > For EXT4, kbbuffers was: > 390999KB for dir creation > 364803KB for dir removal > For XFS, kbbuffers was: > > 1701KB for dir creation > 2738KB for dir removal > > In kernel 2.6, both buffer cache and page cache are merged. The page > cache caches pages of files. The buffer cache caches disk blocks which > consists of mainly metadata (not file data). > > Why is the buffer cache large in case of EXT4 and what is stored in > the buffer cache? XFS does not use buffer cache, while ext[234] does use buffer cache. This is just a different code design. Ext4 uses the buffer cache to track metadata for journaling. Cheers, Andreas-- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
