From 2672bcc9f85ba28ff648e092e9eb4cd9e69ce418 Mon Sep 17 00:00:00 2001 From: Lasse Collin Date: Sun, 7 Mar 2010 13:29:28 +0200 Subject: [PATCH] Increase the default memory usage limit on "low-memory" systems. Previously the default limit was always 40 % of RAM. The new limit is a little bit more complex: - If 40 % of RAM is at least 80 MiB, 40 % of RAM is used as the limit. - If 80 % of RAM is over 80 MiB, 80 MiB is used as the limit. - Otherwise 80 % of RAM is used as the limit. This should make it possible to decompress files created with "xz -9" on more systems. Swapping is generally more expected on systems with less RAM, so higher default limit on them shouldn't cause too bad surprises in terms of heavy swapping. Instead, the higher default limit should reduce the number of bad surprises when it used to prevent decompression of files created with "xz -9". The DoS prevention system shouldn't be a DoS itself. Note that even with the new default limit, a system with 64 MiB RAM cannot decompress files created with "xz -9" without user overriding the limit. This should be OK, because if xz is going to need more memory than the system has RAM, it will run very very slowly and thus it's good that user has to override the limit in that case. --- src/xz/hardware.c | 43 +++++++++++++++++++++++++++++++------------ src/xz/xz.1 | 21 +++++++++++++++------ src/xzdec/xzdec.1 | 8 ++++---- src/xzdec/xzdec.c | 42 ++++++++++++++++++++++++++++++------------ 4 files changed, 80 insertions(+), 34 deletions(-) diff --git a/src/xz/hardware.c b/src/xz/hardware.c index d91b4ce..74742fc 100644 --- a/src/xz/hardware.c +++ b/src/xz/hardware.c @@ -21,6 +21,9 @@ static uint32_t threadlimit; /// Memory usage limit static uint64_t memlimit; +/// Total amount of physical RAM +static uint64_t total_ram; + extern void hardware_threadlimit_set(uint32_t new_threadlimit) @@ -48,11 +51,27 @@ hardware_threadlimit_get(void) extern void hardware_memlimit_set(uint64_t new_memlimit) { - if (new_memlimit == 0) { - // The default is 40 % of total installed physical RAM. - hardware_memlimit_set_percentage(40); - } else { + if (new_memlimit != 0) { memlimit = new_memlimit; + } else { + // The default depends on the amount of RAM but so that + // on "low-memory" systems the relative limit is higher + // to make it more likely that files created with "xz -9" + // will still decompress without overriding the limit + // manually. + // + // If 40 % of RAM is 80 MiB or more, use 40 % of RAM as + // the limit. + memlimit = 40 * total_ram / 100; + if (memlimit < UINT64_C(80) * 1024 * 1024) { + // If 80 % of RAM is less than 80 MiB, + // use 80 % of RAM as the limit. + memlimit = 80 * total_ram / 100; + if (memlimit > UINT64_C(80) * 1024 * 1024) { + // Otherwise use 80 MiB as the limit. + memlimit = UINT64_C(80) * 1024 * 1024; + } + } } return; @@ -65,14 +84,7 @@ hardware_memlimit_set_percentage(uint32_t percentage) assert(percentage > 0); assert(percentage <= 100); - uint64_t mem = lzma_physmem(); - - // If we cannot determine the amount of RAM, use the assumption - // defined by the configure script. - if (mem == 0) - mem = (uint64_t)(ASSUME_RAM) * 1024 * 1024; - - memlimit = percentage * mem / 100; + memlimit = percentage * total_ram / 100; return; } @@ -87,6 +99,13 @@ hardware_memlimit_get(void) extern void hardware_init(void) { + // Get the amount of RAM. If we cannot determine it, + // use the assumption defined by the configure script. + total_ram = lzma_physmem(); + if (total_ram == 0) + total_ram = (uint64_t)(ASSUME_RAM) * 1024 * 1024; + + // Set the defaults. hardware_memlimit_set(0); hardware_threadlimit_set(0); return; diff --git a/src/xz/xz.1 b/src/xz/xz.1 index 9dc354a..aba0a69 100644 --- a/src/xz/xz.1 +++ b/src/xz/xz.1 @@ -5,7 +5,7 @@ .\" This file has been put into the public domain. .\" You can do whatever you want with this file. .\" -.TH XZ 1 "2010-01-15" "Tukaani" "XZ Utils" +.TH XZ 1 "2010-03-07" "Tukaani" "XZ Utils" .SH NAME xz, unxz, xzcat, lzma, unlzma, lzcat \- Compress or decompress .xz and .lzma files .SH SYNOPSIS @@ -195,9 +195,16 @@ is several gigabytes. .PP To prevent uncomfortable surprises caused by huge memory usage, .B xz -has a built-in memory usage limiter. The default limit is 40 % of total -physical RAM. While operating systems provide ways to limit the memory usage -of processes, relying on it wasn't deemed to be flexible enough. +has a built-in memory usage limiter. While some operating systems provide +ways to limit the memory usage of processes, relying on it wasn't deemed +to be flexible enough. The default limit depends on the total amount of +physical RAM: +.IP \(bu 3 +If 40\ % of RAM is at least 80 MiB, 40\ % of RAM is used as the limit. +.IP \(bu 3 +If 80\ % of RAM is over 80 MiB, 80 MiB is used as the limit. +.IP \(bu 3 +Otherwise 80\ % of RAM is used as the limit. .PP When compressing, if the selected compression settings exceed the memory usage limit, the settings are automatically adjusted downwards and a notice @@ -588,9 +595,11 @@ can be specified as a percentage of physical RAM. Example: .IP \(bu 3 The .I limit -can be reset back to its default value (currently 40 % of physical RAM) -by setting it to +can be reset back to its default value by setting it to .BR 0 . +See the section +.B "Memory usage" +for how the default limit is defined. .IP \(bu 3 The memory usage limiting can be effectively disabled by setting .I limit diff --git a/src/xzdec/xzdec.1 b/src/xzdec/xzdec.1 index 442a19e..3057c58 100644 --- a/src/xzdec/xzdec.1 +++ b/src/xzdec/xzdec.1 @@ -4,7 +4,7 @@ .\" This file has been put into the public domain. .\" You can do whatever you want with this file. .\" -.TH XZDEC 1 "2009-06-04" "Tukaani" "XZ Utils" +.TH XZDEC 1 "2010-03-07" "Tukaani" "XZ Utils" .SH NAME xzdec, lzmadec \- Small .xz and .lzma decompressors .SH SYNOPSIS @@ -99,8 +99,7 @@ can be specified as a percentage of physical RAM. Example: .IP \(bu 3 The .I limit -can be reset back to its default value (currently 40 % of physical RAM) -by setting it to +can be reset back to its default value by setting it to .BR 0 . .IP \(bu 3 The memory usage limiting can be effectively disabled by setting @@ -163,6 +162,7 @@ for executables distributed in typical non-embedded operating system distributions. If you need a truly small .B .xz decompressor, consider using XZ Embedded. -.\" TODO: Provide URL to XZ Embedded. .SH "SEE ALSO" .BR xz (1) +.PP +XZ Embedded: diff --git a/src/xzdec/xzdec.c b/src/xzdec/xzdec.c index 2b16686..6ddf7d2 100644 --- a/src/xzdec/xzdec.c +++ b/src/xzdec/xzdec.c @@ -38,6 +38,9 @@ /// Number of bytes to use memory at maximum static uint64_t memlimit; +/// Total amount of physical RAM +static uint64_t total_ram; + /// Error messages are suppressed if this is zero, which is the case when /// --quiet has been given at least twice. static unsigned int display_errors = 2; @@ -103,14 +106,7 @@ version(void) static void memlimit_set_percentage(uint32_t percentage) { - uint64_t mem = lzma_physmem(); - - // If we cannot determine the amount of RAM, use the assumption - // set by the configure script. - if (mem == 0) - mem = (uint64_t)(ASSUME_RAM) * 1024 * 1024; - - memlimit = percentage * mem / 100; + memlimit = percentage * total_ram / 100; return; } @@ -120,15 +116,37 @@ memlimit_set_percentage(uint32_t percentage) static void memlimit_set(uint64_t new_memlimit) { - if (new_memlimit == 0) - memlimit_set_percentage(40); - else + if (new_memlimit != 0) { memlimit = new_memlimit; + } else { + memlimit = 40 * total_ram / 100; + if (memlimit < UINT64_C(80) * 1024 * 1024) { + memlimit = 80 * total_ram / 100; + if (memlimit > UINT64_C(80) * 1024 * 1024) + memlimit = UINT64_C(80) * 1024 * 1024; + } + } return; } +/// Get the total amount of physical RAM and set the memory usage limit +/// to the default value. +static void +memlimit_init(void) +{ + // If we cannot determine the amount of RAM, use the assumption + // defined by the configure script. + total_ram = lzma_physmem(); + if (total_ram == 0) + total_ram = (uint64_t)(ASSUME_RAM) * 1024 * 1024; + + memlimit_set(0); + return; +} + + /// \brief Convert a string to uint64_t /// /// This is rudely copied from src/xz/util.c and modified a little. :-( @@ -422,7 +440,7 @@ main(int argc, char **argv) // Set the default memory usage limit. This is needed before parsing // the command line arguments. - memlimit_set(0); + memlimit_init(); // Parse the command line options. parse_options(argc, argv);