Charles Manning wrote: > On Wednesday 12 August 2009 16:00:40 Andrew McKay wrote: >> Hey Charles, >> >> When testing with the 2GB NAND I was visited by the OOM killer a few times. >> This makes me think we're short on RAM for handling a 2GB NAND part. Our >> board currently has 32MB of RAM, of which 8MB is used for a RAM disk. When >> I dropped the ramdisk down to 3.5MB for testing purposes, I didn't have >> issues with the OOM killer any more. We're looking at moving up to 64MB of >> RAM to avoid this issue. However in the future I'd like to be able to >> estimate the memory usage of YAFFS2 based on NAND size. >> >> I found a thread about YAFFS2 memory usage, and I just want to make sure I >> understand it correctly. >> >> http://www.yaffs.net/lurker/message/20090701.190059.23524635.ca.html#yaffs >> >>> * yaffs_Objects: Each object (file, directory,...) holds a yaffs_Object >> in memory which is around 120 bytes per object. >> >> So every file, directory, etc. uses up 120 bytes of RAM. This is all the >> time? Right from when the filesystem is mounted? So if I have 1000 objects >> on the device I'll be using up 120000 bytes? >> >>> * yaffs_Tnodes: These are the things used to build the trees. >> The part I'm using is 8192 erase blocks, and 64 pages per erase block. >> That means there are 524288 chunks in my filesystem. Using your equation I >> come up with >> >> Log2(524288) = 19 bits >> 19 + 1 = 20 (which is already even) >> >> So 20 bits will be used to represent each chunk. >> >> Assuming worst case and the filesystem is full I will be using all 524288 >> chunks. This means that I will need 20 * 512K which is 10MB of RAM to >> store all the Tnodes. Does that seem about right? > > Bits mate, not bytes... Therefore that calc should come out to be closer to > 1.2Mbytes > > The calculation is somewhat complicated by the fact that Tnodes are managed in > arrays of 16, ie 40 bytes in this case. Thus: > * On average larger files will have a wasted 20 bytes of Tnode. > * Very small files will still need 40 bytes of Tnode, even if they only use a > small amount of that. > > Thus lots of small files will skew the numbers a bit. > > If you do a /proc/yaffs you can get the actual numbers in use and use those > > nTnodesCreated * 40 bytes > + > nObjectsCreated * approx 120 bytes > > It would be possible to make a tweak to handle very short files better. Files > smaller than 1 chunk don't really need a tnode tree since the tnode pointer > could be stored directly in the object structure. Base on your experience do you have a rule of thumb for amount of RAM required based on the size or number of chunks of NAND? Thanks, Andrew McKay Iders Inc.