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Date: Sun, 17 Feb 2013 09:34:15 +0530 From: Subranshu Patel <spatel.ml@...il.com> To: linux-ext4@...r.kernel.org Subject: Large buffer cache in EXT4 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? -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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