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bufview(1)							    bufview(1)

NAME    [Toc]    [Back]

     bufview - file system buffer cache	activity monitor

SYNOPSIS    [Toc]    [Back]

     bufview [ -options	]

DESCRIPTION    [Toc]    [Back]

     bufview displays periodic information about the file system buffer	cache.
     It	is modeled after the program top(1) which displays information about
     running processes.

OPTIONS    [Toc]    [Back]

     -b	  Use batch (or	non-interactive	mode).

     -s	delay
	  Wait delay seconds between updates.  The default is 3	seconds.

     -d	count
	  Update the display count times and then exit.	 The default is	to
	  continually update.

     -n	lines
	  Display only lines number of buffers.	 The default is	to display as
	  many buffers as will fit the screen when in interactive mode,	or all
	  buffers when in batch	mode.

     -f	flags
	  Only display buffers which have the specified	flags bits set.

     -o	order
	  display buffers using	the specified sort order.

     -S	  Do not display system	buffers.

     -D	  Do not display data buffers.

INTERACTIVE MODE    [Toc]    [Back]

     bufview accepts display commands interactively.  These commands are
     currently recognized:

     ^L	  Redraw the screen.

     h or ?
	  Display a summary of the commands (help screen).

     q	  Quit.

     s	  Change number	of seconds to delay between updates.

     S	  Toggle display of system buffers on or off.

									Page 1

bufview(1)							    bufview(1)

     D	  Toggle display of file data buffers on or off.

     o	  Specify buffer display order (see details below).

     f	  Display only buffers with specific state flags set (see details

     F	  Ignore buffer	state flags when determining which buffers to display.

     m	  Display only buffers from the	specified device (mounted file

     M	  Display buffers from all mounted file	systems.  This is the default

FILE SYSTEM BUFFERS    [Toc]    [Back]

     There are a set number of buffer headers allocated	by the system when it
     starts up,	but the	memory attached	to each	buffer changes over time.

     In	the Irix operating system, a distinction is made between data buffers,
     which hold	the data from regular files, and system	or meta-data buffers,
     which hold	the file system	control	data, such as directories, inodes and
     file system mapping information.

     The file system buffer cache is integrated	with the memory	page
     allocator.	 Any pages which contain file system data are remembered; if
     the pages are released from a buffer header because the buffer is asked
     to	represent different data, the pages can	be reclaimed by	another	buffer
     later if the pages	haven't	been reused in the meantime.  Thus pages of
     memory which hold file data can be: attached to buffers; or attached to
     one or more user processes	(see mmap(2)), separately or at	the same time;
     or	on the free page list.


     The first few lines of the	display	monitor	system-wide statistics.	 These
     include buffer counts, memory values, events and time values.

     The total number of buffers is displayed as Bufs; at any moment, each of
     these buffers is accounted	for as either Sys, Data, Empty or Inact.  Sys
     means that	the buffer contains file system	meta-data; a Data buffer hold
     regular file data.	 Empty implies that the	buffer does not	have any data
     stored at the moment; Inact means that the	buffer is empty	and has	been
     removed from use temporarily to avoid having the buffer cache use too
     much memory.

     The total amount of system	memory is displayed as Mem.  The amount	of
     memory associated with Sys	and Data buffers is displayed as SMem and
     DMem.  The	current	amount of free memory is displayed as MFree; the
     portion of	that memory that holds (reclaimable) file system data is shown
     as	MFreD.

									Page 2

bufview(1)							    bufview(1)

     Various system memory limiters are	also shown.  The operating system
     avoids having the amount of memory	in Data	buffers	grow too large.	 To
     such end, the system tuneable parameter, min_free_pages, specifies	how
     many pages	should be on the free list.  If	there are fewer, the Data
     buffers will be trimmed, but only as low as min_file_pages	(see
     systune(1)).  min_file_pages and min_free_pages are shown,	as memory
     amounts, in DMin and FrMin.

     There are two other limits	to the amount of memory	the buffer Data	cache
     can use.  There are two system counters known as availrmem	and availsmem,
     which indicate, respectively, how many physical pages would be available
     if	push came to shove (that is, if	the system paging daemon were to push
     every possible user page out of memory and	in to backing store); and how
     many pages	of memory and backing store (swap) have	not been reserved by
     programs and the kernel.  These two counters are expressed	as memory
     amounts by	MaxR and MaxS.	In the 6.5 operating system release, Data
     buffer pages are not accounted for	in either availrmem or availsmem, but
     since the Data cache can never be forced to drop below min_file_pages,
     the system	must ensure that: first, neither availrmem nor availsmem drop
     below min_file_pages; and second, that if the Data	cache grows beyond
     min_file_pages, it	does not grow beyond the avail counters.  These	values
     are displayed as a	diagnostic tool	to help	understand whether there are
     enough buffers allocated for the system, whether the cache	is responding
     well enough to various memory pressures, and whether the tuneable
     parameters	are configured sanely.

     If	the buffer cache memory	must be	trimmed, individual buffer headers are
     inactivated.  Inactivated buffers,	displayed as Inact are those which are
     both trimmed of their memory and also removed from	the buffer free	lists
     so	that won't be immediately refilled to represent	other file system
     data.  When the system decides that the amount of memory allocated	to
     buffers can grow, and there are no	empty buffers available, inactive
     buffers are activated (put	back on	a free list).

     Some event	counters are also shown.  The number of	times a	buffer is
     inactivated is shown as deact; conversly, reactivations are shown as

     The number	of times a particular buffer is	sought is given	as gtblk; the
     times a sought buffer is found in the cache is found.  If a particular
     buffer isn't found	in the buffer cache, a buffer free list	is searched
     for the first available buffer that can be	reclaimed.  Buffers that have
     delayed write data	or that	have special release functions associated with
     them are not directly acquired in the search for available	buffers;
     instead they are written (write) or the release function is called
     (relse), and skipped.  Buffers have a counter which, when set, allows the
     buffer to pass through the	free list search unscathed (the	counter	is
     decremented each time it is examined).  The counter stky indicated	these
     events.  Note that	all event counters are given as	events per second
     since the display was last	updated.

									Page 3

bufview(1)							    bufview(1)

     The current time is also shown, as	well as	the current system clock tick

     Note that all event counters are labeled with names that contain no
     upper-case	letters, and that all memory values are	labeled	with names
     that contain an upper-case	'M'.  With memory values, a 'K'	represents
     1024 bytes, an 'M'	is 1024	K and so on.  Buffer counters are given	as
     decimal values, and their labels all start	with upper-case	characters.

     The display sort order and	any pruning flags are also displayed.  The
     sort order	determines in what order buffers are to	be displayed; and
     pruning flags, if specified, indicated that bufview should	only display
     buffers with the indicated	flags set.  The	following sort keys can	be

	  m    display the files with the most buffers attached
	  l    display the files with the least	buffers	attached
	  b    display the biggest buffers first
	  s    display the smallest buffers first
	  n    display the newest buffers first
	  o    display the oldest buffers first

     Note that bufview can be in either	aggregate mode or itemized mode.  When
     in	aggregate mode,	all files (for regular file data) or devices (for
     system data) that are currently using buffers are represented as a	single
     buffer; in	itemized mode, individual buffers are presented.  By default,
     bufview runs in aggregate mode and	sorts using m and b as the sort	keys.
     The display order can be changed, either interactively or as a
     command-line option.  Either way, the last	order specifier	given becomes
     the first sort key.

     If	any pruning flags are requested, only those buffers which have the
     corresponding flags set will be displayed.	 The following pruning flags
     can be specified:

	  dw   display delayed write buffers
	  bsy  display in-use (busy) buffers
	  as   display buffers being used for asynchronous reads/writes
	  na   display NFS buffers being used for async	reads/writes
	  da   display buffers without allocated backing-store
	  nc   display NFS3 buffers without committed backing-store
	  swp	    display buffers being used to swap user pages
	  inact	    display inactive buffers
	  ino	    display inode buffers
	  inomap    display inode map buffers
	  dir_bt    display buffers containing directory btrees
	  map	    display buffers containing maps
	  attr_bt   display attribute btree buffers
	  agi	    display buffers containing AG header (inode	allocation)
	  agf	    display allocation group header buffers
	  agfl	    display allocation group free block	array buffers

									Page 4

bufview(1)							    bufview(1)

	 dquot	    display quota buffers containing dquot structures

     These, too, can be	specified as command-line options or demanded
     interactively.  Further, pruning flags can	be removed (wholesale) with
     the F interactive command.

     If	a display order	or flag	specifier is given that	is incompatible	with
     the current mode, the mode	changes	and any	incompatible sort or display
     directives	are removed.  For example, the n display order and all pruning
     flags are incompatible with aggregate mode; if any	of these are
     specified,	m or l will be removed as a sort key.  Similarly, if either m
     and l are demanded, bufview will convert to aggregate mode, and any
     pruning flags or itemized sort keys will be deleted.

THE DISPLAY    [Toc]    [Back]

     The information displayed about buffers changes depending whether bufview
     is	in aggregate mode or itemized mode.  In	either mode, the internal node
     number of the file	is displayed under the column VNUMBER for data
     buffers, or listed	simply as a 'system' file if the buffer	represents a
     meta-data buffer.

     In	aggregate mode,	the next column	is NAME.  Only data file names are
     given, and	only those whose names are brief enough	to be included in the
     system's internal directory name cache (currently 31 bytes).  The names
     displayed by bufview are truncated.  A file whose name is too large to
     fit in the	name cache is displayed	as '?';	if the system cannot determine
     the name of the file because it would have	had to sleep waiting for an
     internal lock, the	file names is displayed	as '??'.  In itemized mode the
     column NAME/REF shows either the (possibly	truncated) file	name or, for
     meta-data buffers,	a pseudo-reference counter which, if non-zero, allows
     a buffer a	free trip though the buffer free list.

     The column	DEVICE gives the last component(s) of the file system path
     name of the device	from which the file system for the given buffer's file
     is	mounted.

     The column	FSTYP gives an indication of the type of file system that is
     being managed by the buffer.

     In	aggregate mode,	the next column	is NBUF, which is the number of
     buffers currently holding data or meta-data for the particular file or
     file system, respectively.	 The aggregate buffer size and the amount of
     buffer memory which is delayed-write is shown as SIZE and DELWRI.
     (Delayed write means that the buffer has been altered but the new
     contents have not yet been	written	to backing store.)

     The final two columns in aggregate	mode, LOW and HIGH, represent the
     lowest and	highest	bytes represented by the buffers mapping the object.
     For data buffers, they refer to logical offsets within the	file; for
     meta-data buffers,	offsets	within the file	system.

									Page 5

bufview(1)							    bufview(1)

     In	itemized mode, the index of the	particular buffer in the system's
     buffer array is given as BUF.  Its	size is	given next as SIZE, and	OFFSET
     the offset	within the file	or file	system of the first byte mapped	by the

     The column	AGE shows the clock tick stored	in the buffer.	This value is
     set when the buffer is first created and reset whenever the buffer	is
     accessed or modified.

     Lastly, interesting buffer	flags are shown	under FLAGS.  The list of
     flags which might be displayed are	exactly	those which can	be specified
     as	display	pruning	flags.

FILES    [Toc]    [Back]

     /etc/mtab	    list of mounted file systems

BUGS    [Toc]    [Back]

     The buffer	cache notion of	a device number	does not match that of the
     mounted file system for NFS file systems, so the device number, not its
     name, is displayed.

SEE ALSO    [Toc]    [Back]

     top(1), osview(1)

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