On Thu, Nov 5, 2009 at 3:40 PM, nidhi mittal hada <nidhimittal19@xxxxxxxxx> wrote:
buffer_head data structer does the mapping of existing blocks on disk to pages of RAM.
what does it mean. one or more than one sectors (generally 512 byte) combine together and make a block. filesystem sends the request in terms of block to block layer which goes to I/o scheduler in terms of request queue. After merging and sorting through disk driver it is written on disk in terms of sectors. controller also comes into the picture.
File is a combination of blocks. Generally one block is associated with one buffer in a page into the RAM.
Bio contains Bio-vecs which contains pages ( one or more than one page combined and make a segment). This segmant contains page offset and size. through this all the read/ write happens.
Hi all
i have read about page cache
and about bio biovec page relation too
but in all that i have a minor confusion
what i know is -- pl ignore faults in language used -- its raw -- i know that
1)page consists of many biovecs --
2)each biovec is mentioning continuous data on storage device-- to be transferred
3)many bio vecs coming from different pages -- makes a single bio --
where in a bio contains the request for continuous data (on storage device )
to be transferred ...i understood scatter gather ..i have read things from different place
so
in all that i am missing some links ---
1) How page is related to block on disk ?--
buffer_head data structer does the mapping of existing blocks on disk to pages of RAM.
2) is block concept totally vanished in all this discussion ?
what does it mean. one or more than one sectors (generally 512 byte) combine together and make a block. filesystem sends the request in terms of block to block layer which goes to I/o scheduler in terms of request queue. After merging and sorting through disk driver it is written on disk in terms of sectors. controller also comes into the picture.
3) if a single bio is transferred at a time -- then is bio equivalent to a block ?
or no relation of block and bio ?
4) if bio is equivalent to one block -- then finally we are transferring block only .... then where abt that benefit of shifting from buffer cache to page cache ....isnt it ??
5) page is related to a file -- a single page can contain only one file's data .... is that true ?
File is a combination of blocks. Generally one block is associated with one buffer in a page into the RAM.
or a page can contain some bio_vecs of file1 and some bio_vecs of other file2 ??
Bio contains Bio-vecs which contains pages ( one or more than one page combined and make a segment). This segmant contains page offset and size. through this all the read/ write happens.
pl help in clarification
thanks
nidhi
--
Thanks & Regards
Nidhi Mittal Hada
