Hi Rajat, I am not opposed to creating multiple bio. I just meant to say that if there is another method which involves not breaking the bio (as i understand breaking the bio) i would love to know it. Regards, Neha On Mon, Jan 6, 2014 at 12:23 PM, Rajat Sharma <fs.rajat@xxxxxxxxx> wrote: > Why do you want to avoid creating multiple bio? If you have data on multiple > disks, create multiple of them and shoot them simultaneously to get > advantage of parallel IO. And if it is single disk, elevators of lower disk > would do a good job of reading/writing them in serial order of disk seek. I > don't see much of savings with not creating bio, it is going to be allocated > from slab anyways. Also risks you involve with leaving bio in a corruptible > state after customization for one disk are higher. > > > On Mon, Jan 6, 2014 at 10:03 AM, neha naik <nehanaik27@xxxxxxxxx> wrote: >> >> Hi All, >> I figured out the method by some trial and error and looking at the >> linux source code. >> We can do something like this : >> Say we want to read pages of bvec in 512 chunks. Create bio with >> a single page and read 512 chunk of data from wherever you want to (it >> can be different disks). >> >> dst = kmap_atomic(bvec->bv_page, KM_USER0); ---> bvec is of >> original bio >> src = kmap_atomic(page, KM_USER0); ---> page we read by >> creating new bio >> memcpy(dst+offset, src, 512); >> kunmap_atomic(src, KM_USER0); >> kunmap_atomic(dst, KM_USER0); >> >> My difficulty was not being able to access the high memory page in >> kernel. I was earlier trying to increment the offset of the bvec and >> pass the page to the layer below assuming that it would read in the >> data at correct offset but of course it was resulting in panic. The >> above solves that. Of course, if there is some other method which >> involves not creating any bio i would love to know. >> >> Regards, >> Neha >> >> >> On Sat, Jan 4, 2014 at 9:32 AM, Pranay Srivastava <pranjas@xxxxxxxxx> >> wrote: >> > >> > On 04-Jan-2014 5:18 AM, "neha naik" <nehanaik27@xxxxxxxxx> wrote: >> >> >> >> Hi All, >> >> I am getting a request with bvec->bv_len > 512. Now, the >> >> information to be read is scattered across the entire disk in 512 >> >> chunks. So that, information on disk can be : sector 8, sector 100, >> >> sector 9. >> >> Now if i get a request to read with the bvec->bv_len > 512 i need to >> >> pull in the information from >> >> multiple places on disk since the data is not sequentially located. >> >> I tried to look at the linux source code because i think raid must be >> >> doing it all the time. (eg : on disk 1 we may be storing sector 6 and >> >> on disk 2 we may be storing sector 7 and so on). >> > >> > You are right. Perhaps you need to clone the bio and set them properly. >> > I >> > guess you ought to check dm driver's make_request function. It does >> > clone >> > bio. >> > >> > I don't know if you can split that request while handling it. Perhaps >> > reinserting that request could work. >> > >> >> However, i have not really got any useful information from it. Also >> >> scouring through articles on >> >> google has not helped much. >> >> I am hoping somebody points me in the right direction. >> >> >> >> Thanks in advance, >> >> Neha >> >> >> >> _______________________________________________ >> >> Kernelnewbies mailing list >> >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> > >> > ---P.K.S >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
