160 lines
6.0 KiB
Diff
160 lines
6.0 KiB
Diff
From 55f7ba830d40d438f0b0663a505e0c227fc68b6b Mon Sep 17 00:00:00 2001
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From: Phillip Lougher <phillip@squashfs.org.uk>
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Date: Tue, 10 Jun 2014 21:51:52 +0100
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Subject: mksquashfs: fix phys mem calculation for 32-bit processes on
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PAE/64-bit kernels
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When adding the code to base default memory usage on physical memory
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(by default use 25% of physical memory), I made an oversight. I assumed
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the process would be able to address 25% of physical memory.
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However, for 32-bit processes running on a PAE kernel or 64-bit kernel,
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25% of physical memory can easily exceed the addressible memory for a
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32-bit process, e.g. if a machine has 24 GB of physical memory, the
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code would asume the process could easily use 6 GB.
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A 32-bit process by definition can only address 4 GB (32-bit pointers).
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But, due to the typical kernel/user-space split (1GB/3GB, or 2GB/2GB)
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on PAE kernels, a 32-bit process may only be able to address 2 GB.
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So, if Mksquashfs is a 32-bit application running on a PAE/64-bit kernel,
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the code assumes it can address much more memory than it really can, which
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means it runs out of memory.
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The fix is to impose a maximum default limit on 32-bit kernels, or
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otherwise to never use a value more than 25% of the address space. If
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we assume the maximum address space is 2 GB, then the maximum becomes
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512 MB. But, given most kernels used the 1GB/3GB split, that may be
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unduely conservative, and 25% of 3 GB (756 MB) may be better. This
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patch compromises on 640 MB, which is mid-way between the 512 MB and 756 MB
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values. It is also the fixed default value previously used by Mksquashfs.
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This patch also alters the code which imposes a maximum size. Previously
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it was believed limiting to the physical memory size was adequate. But
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obviously this needs to be updated to take into account a 32-bit process
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may only be able to address 2 GB. In the process I've also taken the
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opportunity to limit all requests to no more than 75% of physical memory.
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Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
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diff --git a/squashfs-tools/mksquashfs.c b/squashfs-tools/mksquashfs.c
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index 86f82bb..5370ecf 100644
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--- a/squashfs-tools/mksquashfs.c
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+++ b/squashfs-tools/mksquashfs.c
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@@ -304,7 +304,7 @@ void restorefs();
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struct dir_info *scan1_opendir(char *pathname, char *subpath, int depth);
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void write_filesystem_tables(struct squashfs_super_block *sBlk, int nopad);
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unsigned short get_checksum_mem(char *buff, int bytes);
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-int get_physical_memory();
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+void check_usable_phys_mem(int total_mem);
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void prep_exit()
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@@ -4053,11 +4053,7 @@ void initialise_threads(int readq, int fragq, int bwriteq, int fwriteq,
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BAD_ERROR("Queue sizes rediculously too large\n");
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total_mem += fwriteq;
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- if(total_mem > get_physical_memory()) {
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- ERROR("Total queue sizes larger than physical memory.\n");
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- ERROR("Mksquashfs will exhaust physical memory and thrash.\n");
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- BAD_ERROR("Queues too large\n");
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- }
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+ check_usable_phys_mem(total_mem);
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/*
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* convert from queue size in Mbytes to queue size in
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@@ -4879,6 +4875,72 @@ int get_physical_memory()
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}
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+void check_usable_phys_mem(int total_mem)
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+{
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+ /*
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+ * We want to allow users to use as much of their physical
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+ * memory as they wish. However, for practical reasons there are
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+ * limits which need to be imposed, to protect users from themselves
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+ * and to prevent people from using Mksquashfs as a DOS attack by using
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+ * all physical memory. Mksquashfs uses memory to cache data from disk
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+ * to optimise performance. It is pointless to ask it to use more
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+ * than 75% of physical memory, as this causes thrashing and it is thus
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+ * self-defeating.
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+ */
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+ int mem = get_physical_memory();
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+
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+ mem = (mem >> 1) + (mem >> 2); /* 75% */
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+
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+ if(total_mem > mem) {
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+ ERROR("Total memory requested is more than 75%% of physical "
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+ "memory.\n");
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+ ERROR("Mksquashfs uses memory to cache data from disk to "
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+ "optimise performance.\n");
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+ ERROR("It is pointless to ask it to use more than this amount "
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+ "of memory, as this\n");
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+ ERROR("causes thrashing and it is thus self-defeating.\n");
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+ BAD_ERROR("Requested memory size too large\n");
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+ }
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+
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+ if(sizeof(void *) == 4 && total_mem > 2048) {
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+ /*
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+ * If we're running on a kernel with PAE or on a 64-bit kernel,
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+ * then the 75% physical memory limit can still easily exceed
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+ * the addressable memory by this process.
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+ *
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+ * Due to the typical kernel/user-space split (1GB/3GB, or
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+ * 2GB/2GB), we have to conservatively assume the 32-bit
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+ * processes can only address 2-3GB. So refuse if the user
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+ * tries to allocate more than 2GB.
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+ */
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+ ERROR("Total memory requested may exceed maximum "
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+ "addressable memory by this process\n");
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+ BAD_ERROR("Requested memory size too large\n");
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+ }
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+}
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+
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+
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+int get_default_phys_mem()
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+{
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+ int mem = get_physical_memory() / SQUASHFS_TAKE;
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+
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+ if(sizeof(void *) == 4 && mem > 640) {
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+ /*
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+ * If we're running on a kernel with PAE or on a 64-bit kernel,
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+ * the default memory usage can exceed the addressable
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+ * memory by this process.
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+ * Due to the typical kernel/user-space split (1GB/3GB, or
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+ * 2GB/2GB), we have to conservatively assume the 32-bit
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+ * processes can only address 2-3GB. So limit the default
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+ * usage to 640M, which gives room for other data.
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+ */
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+ mem = 640;
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+ }
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+
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+ return mem;
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+}
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+
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+
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void calculate_queue_sizes(int mem, int *readq, int *fragq, int *bwriteq,
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int *fwriteq)
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{
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@@ -4890,7 +4952,7 @@ void calculate_queue_sizes(int mem, int *readq, int *fragq, int *bwriteq,
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#define VERSION() \
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- printf("mksquashfs version 4.3 (2014/05/12)\n");\
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+ printf("mksquashfs version 4.3-git (2014/06/09)\n");\
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printf("copyright (C) 2014 Phillip Lougher "\
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"<phillip@squashfs.org.uk>\n\n"); \
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printf("This program is free software; you can redistribute it and/or"\
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@@ -4918,7 +4980,7 @@ int main(int argc, char *argv[])
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int fragq;
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int bwriteq;
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int fwriteq;
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- int total_mem = get_physical_memory() / SQUASHFS_TAKE;
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+ int total_mem = get_default_phys_mem();
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int progress = TRUE;
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int force_progress = FALSE;
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struct file_buffer **fragment = NULL;
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--
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cgit v0.10.1
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