Messages in this thread | | | Date | Wed, 16 Feb 2005 10:03:22 -0800 | From | Martin Bogomolni <> | Subject | kernel 2.4 inode/dentry cache not clearing on umount? |
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Also .. David :
Are you saying that, on a system with 256Megs of ram, of which the kernel is reporting only 3-4Mb free because the inode/dentry caches are taking up most of the memory, and NO page/swap file....
char *p; p = (char *) malloc( 64*1024*1024 );
I assure you that under these conditions, the malloc( ) will fail with NULL.
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Now, in the meantime I have discovered that merely unmounting the filesystem is not enough to clear the dcache and icache.
However, if I unmount the filesystem then run:
cat /dev/hda > /dev/null
This causes the inode/dentry cache to finally shrink and the amount of available free memory increases back to ~200Mb. However, this reduction does not immediately take place when the filesystem is unmounted, and while the filesystem is mounted .. the inode/dentry cache does not shrink and leaves only 3Mb of available free memory.
On Wed, 16 Feb 2005 09:16:40 -0800, Martin Bogomolni <martinbogo@gmail.com> wrote: > Dick, > > I should say that the malloc() succeeds, but the 16mb I need for the > buffer are not available. Since there is no swap/page file in the > embedded environment, there isn't enough memory left afterwards for > the buffer. > > After taking another look at the problem, the kernel has a lot of > memory tied up in the inode and dentry cache. I've tuned > /proc/sys/vm/vm_cache_scan_ratio, vm_mapped_ratio, vm_vfs_scan_ratio > with no real success in shrinking the amount of memory used by these > caches. > > Is there a way to tune and shring the overall amount of memory the > kernel attempts to use for the dentry/inode cache, or make it much, > much more aggressive at clearing it? > > -Martin > > > On Wed, 16 Feb 2005 12:00:53 -0500 (EST), linux-os > <linux-os@analogic.com> wrote: > > On Wed, 16 Feb 2005, Martin Bogomolni wrote: > > > > [SNIPPED...] > > > > > after the 'find' command is run. malloc( ) fails to allocate > > > afterwards. so the kernel does not free any of the missing RAM for > > > malloc( ). > > > > > > > Whatever program is using malloc() is either corrupting > > its buffers or has a memory leak. > > > > Malloc() will always succeed even if the kernel has no > > memory available. This is because the actual allocation > > only occurs when the program attempts to write to one > > of those pages malloc() "promised". > > > > When you look at kernel memory after using `find` everything, > > the directory of everything you have accessed remains in > > memory until the kernel needs page(s) to give to processes. > > > > So, the bottom line is, if malloc() returns NULL, you have > > a problem with your program. It has nothing to do with > > the kernel and "discovering" that the kernel has used > > all available RAM for temporary buffers is not interesting. > > > > [SNIPPED...] > > > > Cheers, > > Dick Johnson > > Penguin : Linux version 2.6.10 on an i686 machine (5537.79 BogoMips). > > Notice : All mail here is now cached for review by Dictator Bush. > > 98.36% of all statistics are fiction. > > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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