Re: Overcommit (OOM) problem on embedded device (PPChameleon)
From: Martin Egholm Nielsen <hidden>
Date: 2005-03-31 20:13:25
Hi David,
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Look in mm/mmap.c and search for overcommit_memory, then do same in the sources for your redhat kernels.I'll look into RH kernel to see if it isn't like you say :-)quoted
Perhaps there's a patch for it floating around somewhere? ;-)Now, that would be really nice. Though I have no idea of where to look!?Here is what I do. Patch is against BK linuxppc-2.4 version 1.1285 (2.4.28-pre3) but might work.
Well, the patch goes straight into my 2.4.20 ppc-kernel - but we have to wait until tomorrow to see if it does the magic.
Burns 5% of the RAM but alternatives all seem worse and I never
I can live with that (3%)...
If you find out why RH works it would be interesting ... perhaps there is a better way.
I downloaded the 2.4.20-10 kernel SRPM from RH8 - it contains all the patches they apply to the serene 2.4.20 kernel. There is some stuff regarding introducing the "overcommit_memory_accounting" variable from the 2.5 kernel, but I haven't looked into it in depth. I'll try with your patch first :-) BR, Martin Egholm
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# # mm/mmap.c # Add pessimistic overcommit mode similar to 2.6 mode 2. # This allows malloc aka sbrk() to actually fail before # process is killed. # Overloaded sysctl_overcommit_memory to be both enable # and ratio to avoid making a new sysctl. # diff -Nru a/mm/mmap.c b/mm/mmap.c--- a/mm/mmap.c 2005-03-30 07:15:13 -08:00 +++ b/mm/mmap.c 2005-03-30 07:15:13 -08:00@@ -45,9 +45,13 @@ __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111 }; -int sysctl_overcommit_memory; +int sysctl_overcommit_memory = 98; + int max_map_count = DEFAULT_MAX_MAP_COUNT; +extern unsigned long totalram_pages; +extern unsigned long totalhigh_pages; + /* Check that a process has enough memory to allocate a * new virtual mapping. */@@ -66,7 +70,7 @@ unsigned long free; /* Sometimes we want to use more memory than we have. */ - if (sysctl_overcommit_memory) + if (sysctl_overcommit_memory == 1) return 1; /* The page cache contains buffer pages these days.. */@@ -91,7 +95,20 @@ free += (dentry_stat.nr_unused * sizeof(struct dentry)) >>PAGE_SHIFT; free += (inodes_stat.nr_unused * sizeof(struct inode)) >> PAGE_SHIFT; + /* + * Leave the last 3% for root + */ + if (current->euid) + free -= free / 32; + + /* Strict mode do not allocate last bit of memory */ + if (sysctl_overcommit_memory) { + pages += (totalram_pages - totalhigh_pages) + * (100 - sysctl_overcommit_memory) / 100; + } + return free > pages; + } /* Remove one vm structure from the inode's i_mapping address space. */