On Thu, Oct 10, 2013 at 6:00 PM, Greg Freemyer <[email protected]>wrote:
> > > Mandeep Sandhu <[email protected]> wrote: > >On Thu, Oct 10, 2013 at 5:00 PM, Ulka Vaze <[email protected]> wrote: > > > >> Hi, > >> disk cache is same as filesystem cache. Also called buffer cache. > >> This is implemneted below fs layer. > >> It is basically a cache of disk blocks mainatined in RAM. (In pages) > >> called buffers. > >> > > > >Ok. So this won't contain "files" but rather "blocks" many of which > >will > >represent a single file? > > The buffer cache knows nothing about files. It may happen to contain the > blocks that correspond to a complete file, but the buffer cache doesn't > have any way to know that. > > >> The purpose of this cache is to improve performance as disk devices > >are > >> slow. > >> You can access this cache from the kernel. > >> Block layer accesses this from the request structure and commits > >blocks on > >> disk. > >> There are more layers in between like IOschedulers / SCSI etc. > >> > > > >Where does the mapping for file to disk pages/blocks exist? Is it in > >the > >inode or dentry entries or something else? > > That is a very filesystem dependent question. > > In general dentry entries point to inodes and inodes point to blocks of > pointers. Those pointers point to actual data blocks. > > You need to discuss a specific filesystem type to even start to discuss > anything specific. > > Ie. Does the fat filesystem have an equivalent of inodes? > > >> How does your device accesses files ? > >> > > > >The device itself runs stripped down version of a fairly recent Linux > >version (3.x). It has DMA capabilities to transfer content to/from the > >hosts memory from/to it's own. > > If 3.x is really current you have 2 more options at least: dm-cache and > bcache. > > I don't know much about either, but they are going to be better options > for I think than the traditional buffer cache. > Greg > -- > Sent from my Android phone with K-9 Mail. Please excuse my brevity. > Ulka, Greg, Thanks a lot for your inputs. I have a lot of reading up to do, so I'll come back if have any specific doubts. Thanks again. Regards, -mandeep
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