Messages in this thread | | | Subject | Re: [PATCH] mm: don't cap request size based on read-ahead setting | From | Jens Axboe <> | Date | Wed, 16 Nov 2016 11:38:20 -0700 |
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On 11/16/2016 08:12 AM, Jens Axboe wrote: > On 11/16/2016 12:17 AM, Hillf Danton wrote: >> On Wednesday, November 16, 2016 12:31 PM Jens Axboe wrote: >>> @@ -369,10 +369,25 @@ ondemand_readahead(struct address_space *mapping, >>> bool hit_readahead_marker, pgoff_t offset, >>> unsigned long req_size) >>> { >>> - unsigned long max = ra->ra_pages; >>> + unsigned long io_pages, max_pages; >>> pgoff_t prev_offset; >>> >>> /* >>> + * If bdi->io_pages is set, that indicates the (soft) max IO size >>> + * per command for that device. If we have that available, use >>> + * that as the max suitable read-ahead size for this IO. Instead of >>> + * capping read-ahead at ra_pages if req_size is larger, we can go >>> + * up to io_pages. If io_pages isn't set, fall back to using >>> + * ra_pages as a safe max. >>> + */ >>> + io_pages = inode_to_bdi(mapping->host)->io_pages; >>> + if (io_pages) { >>> + max_pages = max_t(unsigned long, ra->ra_pages, req_size); >>> + io_pages = min(io_pages, max_pages); >> >> Doubt if you mean >> max_pages = min(io_pages, max_pages); > > No, that is what I mean. We want the maximum of the RA setting and the > user IO size, but the minimum of that and the device max command size.
Johannes pointed out that I'm an idiot - a last minute edit introduced this typo, and I was too blind to spot it when you sent that email this morning. So yes, it should of course be:
max_pages = min(io_pages, max_pages);
like the first version I posted. I'll post a v3...
-- Jens Axboe
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