On Oct 25, 2016, at 6:54 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > On Tue, Oct 25, 2016 at 12:21:22AM -0700, Christoph Hellwig wrote: >> On Tue, Oct 25, 2016 at 03:13:17AM +0300, Kirill A. Shutemov wrote: >>> We are going to do IO a huge page a time. So we need BIO_MAX_PAGES to be >>> at least HPAGE_PMD_NR. For x86-64, it's 512 pages. >> >> NAK. The maximum bio size should not depend on an obscure vm config, >> please send a standalone patch increasing the size to the block list, >> with a much long explanation. Also you can't simply increase the size >> of the largers pool, we'll probably need more pools instead, or maybe >> even implement a similar chaining scheme as we do for struct >> scatterlist. > > The size of required pool depends on architecture: different architectures > has different (huge page size)/(base page size). > > Would it be okay if I add one more pool with size equal to HPAGE_PMD_NR, > if it's bigger than than BIO_MAX_PAGES and huge pages are enabled? Why wouldn't you have all the pool sizes in between? Definitely 1MB has been too small already for high-bandwidth IO. I wouldn't mind BIOs up to 4MB or larger since most high-end RAID hardware does best with 4MB IOs. Cheers, Andreas
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