Messages in this thread | | | Date | Sun, 22 Mar 2015 18:24:50 +0200 | From | Boaz Harrosh <> | Subject | Re: [RFC PATCH 0/7] evacuate struct page from the block layer |
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On 03/20/2015 10:31 PM, Matthew Wilcox wrote: <> > > There's a lot of code out there that relies on struct page being PAGE_SIZE > bytes.
Not so much really. Not at the lower end of the stack. You can actually feed a vp = kmalloc(64K); bv_page = virt_to_page(vp) bv_len = 64k
And feed that to an hard drive. It works.
The only last stronghold of PAGE_SIZE is at the page-cache and page-fault granularity where the minimum is the better. But it should not be hard to clean up the lower end of the stack. Even introduce a: page_size(page)
You will find that every subsystem that can work with a sub-page size similar to above bv_len. Will also work well with bigger than PAGE_SIZE bv_len equivalent.
Only the BUG_ONs need to convert to page_size(page) instead of PAGE_SIZE
> I'm cool with replacing 'struct page' with 'struct superpage' > [1] in the biovec and auditing all of the code which touches it ... but > that's going to be a lot of code! I'm not sure it's less code than > going directly to 'just do I/O on PFNs'. >
struct page already knows how to be a super-page. with the THP mechanics. All a page_size(page) needs is a call to its section, we do not need any added storage at page-struct. (And we can cache this as a flag we actually already have a flag)
It looks like you are very trigger happy to change "biovec and auditing all of the code which touches it"
I believe long long term your #1b is the correct "full audit" path:
Page Is the virtual-2-page-2-physical descriptor + state. It is variable size
> [1] Please, somebody come up with a better name!
sure struct page *page.
The one to kill is PAGE_SIZE. In most current code it can just be MIN_PAGE_SIZE and CACHE_PAGE_SIZE == MIN_PAGE_SIZE. Only novelty is enhance of the split_huge_page in the case of "page-fault-granularity".
Thanks Boaz
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