On Tue, Jul 26, 2016 at 02:32:31PM +0200, Stefan Bader wrote: > On 26.07.2016 12:21, Kent Overstreet wrote: > > On Tue, Jul 26, 2016 at 11:51:25AM +0200, Stefan Bader wrote: > >> On 21.07.2016 10:58, Stefan Bader wrote: > >>> I was pointed at the thread which seems to address the same after > >>> I wrote most of below text. Did not want to re-write this so please > >>> bear with the odd layout. > >>> > >>> https://www.redhat.com/archives/dm-devel/2016-June/msg00015.html > >>> > >>> Zhengyuan tries to fix the problem by relocating the superblock on > >>> disk. But I am not sure whether there is really any guarantee about > >>> how __bread fills data into the buffer_head. What if there is the next > >>> odd arch with 128K pages? > >>> > >>> So below is an attempt to be more generic. Still I don't feel completely > >>> happy with the way that a page moves (or is shared) between buffer_head > >>> and biovec. What I tried to outline below is to let the register functions > >>> allocate bio+biovec memory and use the in-memory sb_cache data to initialize > >>> the biovec buffer. > >> > >> Any opinions here? Also adding LKML as I don't seem to get through moderation on > >> dm-devel. > > > > The correct solution is to rip out the __bread() and just read the superblock by > > issuing a bio, the same way all the other IO in bcache is done. > > > > This is the way it's done in the bcache-dev branch - unfortunately, the patch > > that does that in bcache-dev is big and invasive and probably not worth the > > hassle to backport: > > > > https://evilpiepirate.org/git/linux-bcache.git/commit/?h=bcache-dev&id=303eb67bffad57b4d9e71523e7df04bf258e66d1 > > I agree that this looks better and also rather large. > > > > Probably best to just do something small and localized. > > > So what did you think about the change I did? It seemed to be ok for 4K and 64K > at least and is rather small. And I believe that, compared to Zhengyuan's > approach this would have the benefit of not changing the superblock sector. So > it would be compatible with previously created superblocks. Too ugly to live. Just kmalloc() 4k, allocate a bio on the stack, set it up, and submit it with submit_bio_wait(). Use virt_to_page(), don't bother with raw pages - you want 4k, not whatever the page size is. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
