On Fri, Apr 07, 2006 at 10:47:39PM +0900, Ken'ichi Ohmichi wrote: > > Hi. Thanks for your comments of an old command of "Partial dump". > I fed back your comments to this new command. > > The old command had problems that it creates crash dump files with > holes, and the files is expanded if they are backed up, or copied using > unappropriate commands. However, just adding ELF header for each > discontiguous data will result in a large number of segment headers. > When I tested this approach, more than 1500 PT_LOAD was created for 1GB > vmcore. >
I was just talking to Dave Anderson and he suggested that lets not filter out pages until and unless we got some significant number of contiguous pages to be filtered out. This way we will reduce the amount of fragmentation and reduce number of PT_LOAD program headers. Diskdump is already using it. suppose we don't filter out a page until we get 256 contiguous pages to be filtered out. Then for a 16G system we shall require 8K PT_LOAD headers in worst case. One 64bit PT_LOAD size is 64bytes. Total PT_LOAD size would be 512K. For worst case number of headers filtered file size would be 8G. So PT_LOAD size is around .003% of file size. Does not look too bad, given the fact we still retain the compatibility with gdb. Zero size pages would be a problem and we shall have to resort to sparse file scheme, you used in previous patch. > Instead, I adopted the diskdump compression format as dump file format. > The diskdump compression format is able to handle discontiguous data > without creating segment headers for each chunk, and can further reduce > the file size because data in each page is now compressed. Moreover, > the current version of crash can handle the resulting dump file without > any modification. > Ok. So here bitmap is being used to keep track of dumped pages. Definitely it is a optimal scheme in terms of smaller file metadata. Disadvantage being that it looses its generic appeal and gdb can not open it. I guess, I would leave the choice to user and introduce a command line option. User can choose what kind of output dump file does he need. An ELF format one or a custom format one. Thanks Vivek
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