On Thu, Sep 15, 2016 at 06:27:10AM -0600, Andreas Dilger wrote: > On Sep 15, 2016, at 5:55 AM, Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > > This patch modifies ext4_mpage_readpages() to deal with huge pages. > > > > We read out 2M at once, so we have to alloc (HPAGE_PMD_NR * > > blocks_per_page) sector_t for that. I'm not entirely happy with kmalloc > > in this codepath, but don't see any other option. > > If you're reading 2MB from disk (possibly from disjoint blocks with seeks > in between) I don't think that the kmalloc() is going to be the limiting > performance factor. If you are concerned about the size of the kmalloc() > causing failures when pages are fragmented (it can be 16KB for 1KB blocks > with 4KB pages), then using ext4_kvmalloc() to fall back to vmalloc() in > case kmalloc() fails. It shouldn't fail often for 16KB allocations, > but it could in theory. Good point. Will use ext4_kvmalloc(). > I also notice that ext4_kvmalloc() should probably use unlikely() for > the failure case, so that the uncommon vmalloc() fallback is out-of-line > in this more important codepath. The only other callers are during mount, > so a branch misprediction is not critical. I agree. But it's out-of-scope for the patchset. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
