IRIX Base Documentation 2002 November

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Text File | 2002-10-03 | 24.3 KB | 397 lines

sssswwwwaaaapppp((((1111MMMM)))) sssswwwwaaaapppp((((1111MMMM)))) NNNNAAAAMMMMEEEE _ssss_wwww_aaaa_pppp - swap administrative interface SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_aaaa _[[[[_----_iiii_]]]]_[[[[_----_pppp_p_r_i_]]]]_[[[[_----_vvvv_v_l_e_n_]]]] _n_a_m_e _[[[[_l_o_w _[[[[_l_e_n_]]]]_]]]] _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_dddd _n_a_m_e/_l_s_w_a_p _[[[[_l_o_w_]]]] _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_llll _[[[[_----_nnnn_]]]]_[[[[_----_ffff_]]]]_[[[[_----_bbbb_]]]] _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_ssss _[[[[_----_bbbb_]]]] _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_mmmm _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_uuuu DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN _ssss_wwww_aaaa_pppp provides a method of adding, deleting, and monitoring the system swap areas used by the memory manager. The following options are recognized: _----_aaaa Add the specified swap resource. _n_a_m_e is the name of the block special partition, for example, _////_dddd_eeee_vvvv_////_dddd_ssss_kkkk_////_dddd_kkkk_ssss_0000_dddd_1111_ssss_1111 or a regular file. Files on NFS mounted file systems are also permitted (see SSSSwwwwaaaappppppppiiiinnnngggg ttttoooo NNNNFFFFSSSS FFFFiiiilllleeeessss below). _l_o_w is the offset in 512-byte blocks into the partition/file where the swap area should begin. If _l_o_w is absent, a default of 0 is used. This value is rounded up to a multiple of the system defined swap page size. _l_e_n is the length of the swap area in 512-byte blocks. If _l_e_n is absent, the new swap area will use the entire partition/file. This value is rounded down to a multiple of the system defined swap page size. Files used as swap devices must exist and have been previously grown to the appropriate size (see _mmmm_kkkk_ffff_iiii_llll_eeee(1m)). A maximum of 255 swap resources can be active at a given time. This option can only be used by a privileged user. Swap areas are normally added by modifying the _////_eeee_tttt_cccc_////_ffff_ssss_tttt_aaaa_bbbb file to contain the various files and partitions that should be added when the system is booted. When using the _----_aaaa or _----_mmmm option, _////_eeee_tttt_cccc_////_ffff_ssss_tttt_aaaa_bbbb is scanned for an entry whose _t_y_p_e field contains _ssss_wwww_aaaa_pppp and whose _f_i_l_e_s_y_s_t_e_m field matches _n_a_m_e. _n_a_m_e is made into a full path name. If an entry is found in _////_eeee_tttt_cccc_////_ffff_ssss_tttt_aaaa_bbbb, any supplied options are used to supplement any options given on the command line (e.g. priority). _----_iiii Ignore safety checks. Normally, when adding a block special device as a swap resource, a check is made to try to be certain that the block device does not overlap any existing file systems. This option turns off that check. _----_pppp _p_r_i Swap resources have a priority between 0 and 7 inclusive where lower priority swap resources are allocated from first. Within a priority, allocations are done round-robin. By default, block devices are assigned a priority of 0, files on local file systems are assigned a priority of 2 and files on NFS mounted file systems PPPPaaaaggggeeee 1111 sssswwwwaaaapppp((((1111MMMM)))) sssswwwwaaaapppp((((1111MMMM)))) are assigned a priority of 4. This option is only valid when adding a swap resource. _----_vvvv _v_l_e_n_g_t_h Set the virtual length of the swap area to _v_l_e_n_g_t_h. Normally, if this field is not specified, the amount of logical swap is increased by the size of the physical swap device being added. This option tells the system to increase the logical swap amount by _v_l_e_n_g_t_h. Thus, the difference between _v_l_e_n_g_t_h and the actual size of the device is amount of _v_i_r_t_u_a_l swap that is added. The virtual length must be greater than or equal to the physical length of the swap area. If not specified, the virtual length is set equal to the actual length. See _ssss_wwww_aaaa_pppp_cccc_tttt_llll(2) for a discussion on virtual swap spaces. In general, this option should only be used when there is no other way to get enough swap resources (even via NFS) and it is understood the potential problems creating virtual swap can cause. See the discussion of Logical Swap Space below. _----_dddd Delete the specified swap resource. _n_a_m_e is the name of block special partition, for example, _////_dddd_eeee_vvvv_////_dddd_ssss_kkkk_////_dddd_kkkk_ssss_0000_dddd_1111_ssss_1111 or a regular file. If _n_a_m_e starts with a digit, it is interpreted as the logical swap number of the device to be deleted. This is useful when the file or device directory entry has been inadvertently been removed. _l_o_w is the offset in 512-byte blocks into the swap area to be deleted. If not specified, a default of 0 is used. Using this option marks the swap area as ``INDEL'' (in the process of being deleted). The system will not allocate any new blocks from the area, and will try to free swap blocks from it. The area will remain in use until all blocks from it are freed. This option can be used only by a privileged user. _----_mmmm Add all swap resources specified in _////_eeee_tttt_cccc_////_ffff_ssss_tttt_aaaa_bbbb ( _t_y_p_e field is sssswwwwaaaapppp). An entry with the name ////ddddeeeevvvv////sssswwwwaaaapppp is ignored, as are all entries with the nnnnooooaaaauuuuttttoooo option present. This option is primarily for the system start up script _////_eeee_tttt_cccc_////_iiii_nnnn_iiii_tttt_...._dddd_////_ssss_wwww_aaaa_pppp which, at boot time, adds all the administrator configured swap resources. This option can be used only by a privileged user. _----_uuuu Delete all swap resources except the original boot swap resource. This option is primarily for the system shutdown script _////_eeee_tttt_cccc_////_iiii_nnnn_iiii_tttt_...._dddd_////_ssss_wwww_aaaa_pppp which, at system shutdown time, deletes all the configured swap resources. The original boot swap resource may be explicitly deleted using the ----dddd option. This option can be used only by a privileged user. _----_llll List the status of all the swap areas. The output has either seven or nine columns depending on various options. By default, the listing contains nine columns and all values are in 512 byte blocks. The _----_nnnn option enables a new easier to read output format which defaults to printing the important seven columns (the additional two columns are printed if the _----_ffff option is specified). Values with the _----_nnnn option are printed in either bytes, or with the _----_bbbb option, in PPPPaaaaggggeeee 2222 sssswwwwaaaapppp((((1111MMMM)))) sssswwwwaaaapppp((((1111MMMM)))) 512-byte blocks. The _----_ffff and _----_bbbb options are only recognized when the new output format is specified. _#### The logical swap number. This ranges from 1 to 255. This is column is labeled _llll_ssss_wwww_aaaa_pppp in the default listing format. _pppp_aaaa_tttt_hhhh The path name for the swap area. _dddd_eeee_vvvv The major/minor device number in decimal. This is printed in the default list format or in the new format if the _----_ffff option is present. If the swap resource is a block special device, this major/minor pair refers to the special device itself. If the swap resource is a regular file, the major/minor number is for the underlying file system that the file resides on. If the _s_t_a_t(2) on _pppp_aaaa_tttt_hhhh fails, '?,?' is printed. _pppp_rrrr_iiii The priority of the swap resource. _ssss_wwww_aaaa_pppp_llll_oooo The _s_w_a_p_l_o_w value for the area in 512-byte blocks. This is printed in the default list format or in the new format if the _----_ffff option is present. This value is rounded up to a multiple of the system defined swap page size. _pppp_ssss_wwww_aaaa_pppp The _s_w_a_p_l_e_n value for the area. This value is rounded down to a multiple of the system defined swap page size. This is column is labeled _bbbb_llll_oooo_cccc_kkkk_ssss in the default listing format. _ffff_rrrr_eeee_eeee The amount of free swap in the area. _mmmm_aaaa_xxxx_ssss_wwww_aaaa_pppp The maximum size the area will be grown to. _vvvv_ssss_wwww_aaaa_pppp The size over and above any physical space that the system is assuming it can use (see the discussion of logical swap space below, and the _----_vvvv option above). There are four status flags that may be printed after the last column. Normally functioning swap resources will not have any status flags. These flags are: _IIII_NNNN_DDDD_EEEE_LLLL The swap area is being deleted. No allocations will be made from this device. _EEEE_AAAA_CCCC_CCCC_EEEE_SSSS The swap area was on an NFS mounted file system and 'root' does not have permission to write the file. The swap area is immediately taken off line. _EEEE_SSSS_TTTT_AAAA_LLLL_EEEE The swap area was on an NFS mounted file system and the file was removed on the NFS server. The swap area is immediately taken off line. Processes with pages on the swap area will be terminated abnormally the first time they attempt to access any page that had been stored on the swap area. PPPPaaaaggggeeee 3333 sssswwwwaaaapppp((((1111MMMM)))) sssswwwwaaaapppp((((1111MMMM)))) _IIII_OOOO_EEEE_RRRR_RRRR An I/O error occurred on the device. This could result in the abnormal termination of a process. Look in ////vvvvaaaarrrr////aaaaddddmmmm////SSSSYYYYSSSSLLLLOOOOGGGG for more details. Even with I/O errors, the swap area is still allocated from and used until deleted. _----_ssss Print information about total logical swap space usage. Values are printed in either bytes, or with the _----_bbbb option, in 512-byte blocks. _aaaa_llll_llll_oooo_cccc_aaaa_tttt_eeee_dddd The amount of swap space allocated to private pages. _rrrr_eeee_ssss_eeee_rrrr_vvvv_eeee_dddd The amount of swap space not currently allocated, but claimed by private memory mappings. _uuuu_ssss_eeee_dddd The total amount of logical swap space that is either allocated or reserved. _aaaa_vvvv_aaaa_iiii_llll_aaaa_bbbb_llll_eeee The total logical swap space that is currently available for future reservation and allocation. SSSSWWWWAAAAPPPPPPPPIIIINNNNGGGG TTTTOOOO NNNNFFFFSSSS FFFFIIIILLLLEEEESSSS Swapping to regular files on NFS mounted file systems is permitted but should be done only with hard mounted file systems with the _i_n_t_r option turned off (see _ffff_ssss_tttt_aaaa_bbbb(4)). When using either soft mounted file systems or the _i_n_t_r option, NFS may return an error during a swap I/O operation. An I/O error that occurs when swapping in a page causes the process requesting the page to be killed, since it's address space is no longer accessible. Since it is possible for the _iiii_nnnn_iiii_tttt process to be swapped out to the NFS file, a timeout from a soft mounted file system that occurs while the system is swapping in a page for _iiii_nnnn_iiii_tttt will cause _iiii_nnnn_iiii_tttt to die. Since the system is unable to run without _iiii_nnnn_iiii_tttt, the system will in turn panic. Using hard mounted file systems without the _i_n_t_r flag avoids these problems. Even when using hard mounted NFS file systems, the system may appear to hang if the NFS server fails to respond. If the window manager, shell, or other key process is swapped out to the NFS file and the server fails to respond during swap-in, then the system will wait and retry the NFS file read indefinitely. During this time, programs attempting to swap-in pages from that server will not run and will appear to be hung. Once the NFS server starts responding again, normal system activity will resume. Finally, the system administrator must ensure that the swap file on the NFS server is not deleted. This would cause subsequent swap-ins to fail and again cause the associated processes to be killed. LLLLOOOOGGGGIIIICCCCAAAALLLL SSSSWWWWAAAAPPPP SSSSPPPPAAAACCCCEEEE Logical swap space is the sum total of physical memory (less space occupied by the kernel) and all swap devices. The system reserves logical swap space for the private portions of a process's virtual address space (data, bss, stack, MAP_PRIVATE mmap mappings, etc.) when virtual address spaces are created (via _ffff_oooo_rrrr_kkkk(2)), when they are grown (via _bbbb_rrrr_kkkk(2), _ssss_bbbb_rrrr_kkkk(2), or _mmmm_aaaa_llll_llll_oooo_cccc(3C)), or when new segments are attached PPPPaaaaggggeeee 4444 sssswwwwaaaapppp((((1111MMMM)))) sssswwwwaaaapppp((((1111MMMM)))) (via _mmmm_mmmm_aaaa_pppp(2), or _ssss_hhhh_mmmm_aaaa_tttt(2)). Logical swap space is not required for shared text or MAP_SHARED mapped files (except for mappings of the /_d_e_v/_z_e_r_o device). If the amount of private virtual space requested exceeds the available logical swap space, the system call fails with EAGAIN and an "out of logical swap space" message is logged on the console. The system does this in order to prevent memory deadlocks from occurring. Note that the system may report being out of swap space when the _----_llll option shown above reports free swap space available. This happens when the logical swap space has been reserved, but physical space has not yet been allocated, so the blocks are still marked as being free. The _----_ssss option to the _ssss_wwww_aaaa_pppp command will report the amount of logical swap space reserved and allocated. Programs that have large address spaces and large programs that fork, may receive EAGAIN along with the "out of logical swap space" message on the console. This can also happen when debugging a large program with _dddd_bbbb_xxxx or other debugger. There are two ways to avoid this error: adding more real swap space, or adding virtual swap space. Adding real swap space means allocating an additional disk partition or a regular file (either local or remote via NFS) to be used as a swap device (using the _----_aaaa option shown above and the examples below). This is the required approach for programs that use most of the virtual addresses they allocate. The advantage of this approach is that it continues to avoid memory deadlocks, but requires physical disk space to be allocated. The alternative is to add virtual swap space using the _----_vvvv option. This increases the amount of logical swap space without using any physical disk space. This is suitable when the programs involved do not intend to use the virtual address space they allocate (i.e., when the address space is sparse or when a large program that forks intends to exec soon afterwards without modifying many pages). In these cases, physical swap space is not required and so adding virtual swap space allows the kernel to complete the logical swap space reservation and avoid the EAGAIN errors. The advantage of this approach is that it does not require any disk space, but adds the risk of encountering a memory deadlock. Memory deadlocks occur when the system has over-committed logical swap space by allowing the total private virtual space of the processes on the system to exceed real swap space. When processes attempt to use the allocated virtual space, the kernel has no place to store the data (since virtual swap space has no associated disk space), and a memory deadlock results. In these instances, the kernel kills one or more processes to free up enough logical swap space to break the deadlock. For this reason, virtual swap space should not be used in cases where the program will attempt to use the memory. For example, programs that expect _mmmm_aaaa_llll_llll_oooo_cccc(3C) to return _NNNN_UUUU_LLLL_LLLL when there is no more memory will in fact be allocated virtual memory that they could not use without causing a memory deadlock. The _----_vvvv option should therefore be used with care. PPPPaaaaggggeeee 5555 sssswwwwaaaapppp((((1111MMMM)))) sssswwwwaaaapppp((((1111MMMM)))) NNNNOOOOTTTTEEEESSSS The ability to request that a swap resource be automatically grown has not been implemented. EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS The following _ssss_wwww_aaaa_pppp example requests 10K of swap area (twenty 512-byte blocks) on the device _////_dddd_eeee_vvvv_////_dddd_ssss_kkkk_////_dddd_kkkk_ssss_0000_dddd_1111_ssss_1111: _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_aaaa _////_dddd_eeee_vvvv_////_dddd_ssss_kkkk_////_dddd_kkkk_ssss_0000_dddd_1111_ssss_1111 _0000 _2222_0000 The following adds 50Mb of swap space to the system using a file in the /_s_w_a_p directory: _////_uuuu_ssss_rrrr_////_ssss_bbbb_iiii_nnnn_////_mmmm_kkkk_ffff_iiii_llll_eeee _5555_0000_mmmm _////_ssss_wwww_aaaa_pppp_////_ssss_wwww_aaaa_pppp_1111 _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_aaaa _////_ssss_wwww_aaaa_pppp_////_ssss_wwww_aaaa_pppp_1111 To make this swap area permanent (automatically added at boot time) add the following line to /_e_t_c/_f_s_t_a_b: _////_ssss_wwww_aaaa_pppp_////_ssss_wwww_aaaa_pppp_1111 _ssss_wwww_aaaa_pppp _ssss_wwww_aaaa_pppp _pppp_rrrr_iiii_====_3333 _0000 _0000 The following example adds the regular file _ssss_wwww_aaaa_pppp_1111 as a swap resource. Its priority is set to 5, and the system is told that it should add 100 Mbytes (204800 512-byte blocks) to the virtual swap total. The example assumes that _ssss_wwww_aaaa_pppp_1111 is less than 100 Mbytes in length: _////_ssss_bbbb_iiii_nnnn_////_ssss_wwww_aaaa_pppp _----_aaaa _----_pppp _5555 _----_vvvv _2222_0000_4444_8888_0000_0000 _ssss_wwww_aaaa_pppp_1111 The following line in _////_eeee_tttt_cccc_////_ffff_ssss_tttt_aaaa_bbbb will add the same swap resource as the previous example, except that it will occur automatically at system startup time: _////_ssss_wwww_aaaa_pppp_////_ssss_wwww_aaaa_pppp_1111 _ssss_wwww_aaaa_pppp _ssss_wwww_aaaa_pppp _pppp_rrrr_iiii_====_5555_,,,,_vvvv_llll_eeee_nnnn_gggg_tttt_hhhh_====_2222_0000_4444_8888_0000_0000 _0000 _0000 FFFFIIIILLLLEEEESSSS /etc/fstab swap and/or vswap to add at system boot /etc/config/vswap.options sets default size of virtual swap at boot /etc/init.d/swap adds/removes swap and/or vswap at boot/shutdown SSSSEEEEEEEE AAAALLLLSSSSOOOO mkfile(1M), mount(1M), swapctl(2), fstab(4). PPPPaaaaggggeeee 6666