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What-is-pdflush

What is pdflush

pdflush

Linux usually writes data out of the page cache using a process called pdflush. At any moment, between 2 and 8 pdflush threads are running on the system. You can monitor how many are active by looking at /proc/sys/vm/nr_pdflush_threads.

First just have a read at http://gentoo-wiki.com/FAQ_Linux_Memory_Management#Overview_of_memory_management

Linux usually writes data out of the page cache using a process called pdflush.

root@shibu-laptop:/proc/sys/vm# ls -l
total 0
-rw-r--r-- 1 root root 0 2008-01-26 01:05 block_dump
-rw-r--r-- 1 root root 0 2008-01-26 01:05 dirty_background_ratio
-rw-r--r-- 1 root root 0 2008-01-26 01:05 dirty_expire_centisecs
-rw-r--r-- 1 root root 0 2008-01-26 01:05 dirty_ratio
-rw-r--r-- 1 root root 0 2008-01-26 01:05 dirty_writeback_centisecs
-rw-r--r-- 1 root root 0 2008-01-26 01:05 laptop_mode
-rw-r--r-- 1 root root 0 2008-01-26 01:05 legacy_va_layout
-rw-r--r-- 1 root root 0 2008-01-26 01:05 lowmem_reserve_ratio
-rw-r--r-- 1 root root 0 2008-01-26 01:05 max_map_count
-rw-r--r-- 1 root root 0 2008-01-26 01:05 min_free_kbytes
-r--r--r-- 1 root root 0 2008-01-26 01:05 nr_pdflush_threads
-rw-r--r-- 1 root root 0 2008-01-26 01:05 overcommit_memory
-rw-r--r-- 1 root root 0 2008-01-26 01:05 overcommit_ratio
-rw-r--r-- 1 root root 0 2008-01-26 01:05 page-cluster
-rw-r--r-- 1 root root 0 2008-01-26 01:05 swappiness
-rw-r--r-- 1 root root 0 2008-01-26 01:05 swap_token_timeout
-rw-r--r-- 1 root root 0 2008-01-26 01:05 vfs_cache_pressure
root@shibu-laptop:/proc/sys/vm# cat nr_pdflush_threads
2
root@shibu-laptop:/proc/sys/vm# cat /proc/meminfo
MemTotal:       255340 kB
MemFree:         14936 kB
Buffers:          1756 kB
Cached:          49364 kB
SwapCached:       4804 kB
Active:         153852 kB
Inactive:         2204 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       255340 kB
LowFree:         14936 kB
SwapTotal:      425648 kB
SwapFree:       384376 kB
Dirty:              92 kB
Writeback:           0 kB
Mapped:         150992 kB
Slab:            13224 kB
CommitLimit:    553316 kB
Committed_AS:   289696 kB
PageTables:       2000 kB
VmallocTotal:   770040 kB
VmallocUsed:      5020 kB
VmallocChunk:   764916 kB
root@shibu-laptop:/proc/sys/vm#  

As you write out data ultimately intended for disk, Linux caches this information in an area of memory called the page cache. You can find out basic info about the page cache using tools like free, vmstat or top