From: Christoph Hellwig <hch@infradead.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
"Darrick J . Wong" <darrick.wong@oracle.com>,
linux-block@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 04/11] block: Add bio_for_each_thp_segment_all
Date: Tue, 1 Sep 2020 15:50:25 +0100 [thread overview]
Message-ID: <20200901145025.GA23220@infradead.org> (raw)
In-Reply-To: <20200901130525.GK14765@casper.infradead.org>
On Tue, Sep 01, 2020 at 02:05:25PM +0100, Matthew Wilcox wrote:
> > > struct page *page = bvec->bv_page;
> > >
> > > while (length > 0) {
> > > size_t count = thp_size(page) - offset;
> > >
> > > if (count > length)
> > > count = length;
> > > iomap_read_page_end_io(page, offset, count, error);
> > > page += (offset + count) / PAGE_SIZE;
> >
> > Shouldn't the page_size here be thp_size?
>
> No. Let's suppose we have a 20kB I/O which starts on a page boundary and
> the first page is order-2. To get from the first head page to the second
> page, we need to add 4, which is 16kB / 4kB, not 16kB / 16kB.
True.
> I'm not entirely sure the bvec would shrink. On 64-bit systems, it's
> currently 8 bytes for the struct page, 4 bytes for the len and 4 bytes
> for the offset. Sure, we can get rid of the offset, but the compiler
> will just pad the struct from 12 bytes back to 16. On 32-bit systems
> with 32-bit phys_addr_t, we go from 12 bytes down to 8, but most 32-bit
> systems have a 64-bit phys_addr_t these days, don't they?
Actually on those system that still are 32-bit because they are so
tiny I'd very much still expect a 32-bit phys_addr_t. E.g. arm
without LPAE or 32-bit RISC-V.
But yeah, point taken on the alignment for the 64-bit ones.
> That's a bit more boilerplate than I'd like, but if bio_vec is going to
> lose its bv_page then I don't see a better way. Unless we come up with
> a different page/offset/length struct that bio_vecs are decomposed into.
I'm not sure it is going to lose bv_page any time soon. I'd sure like
to, but least time something like that came up Linus wasn't entirely
in favor. Things might have changed now, though and I think it is about
time to give it another try.
next prev parent reply other threads:[~2020-09-01 14:50 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-24 15:16 [PATCH 00/11] iomap/fs/block patches for 5.11 Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 01/11] fs: Make page_mkwrite_check_truncate thp-aware Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 02/11] mm: Support THPs in zero_user_segments Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 03/11] mm: Zero the head page, not the tail page Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 04/11] block: Add bio_for_each_thp_segment_all Matthew Wilcox (Oracle)
2020-08-27 8:44 ` Christoph Hellwig
2020-08-31 19:48 ` Matthew Wilcox
2020-09-01 5:34 ` Christoph Hellwig
2020-09-01 13:05 ` Matthew Wilcox
2020-09-01 14:50 ` Christoph Hellwig [this message]
2020-08-24 15:16 ` [PATCH 05/11] iomap: Support THPs in iomap_adjust_read_range Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 06/11] iomap: Support THPs in invalidatepage Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 07/11] iomap: Support THPs in read paths Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 08/11] iomap: Change iomap_write_begin calling convention Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 09/11] iomap: Support THPs in write paths Matthew Wilcox (Oracle)
2020-08-24 15:16 ` [PATCH 10/11] iomap: Inline data shouldn't see THPs Matthew Wilcox (Oracle)
2020-08-24 15:17 ` [PATCH 11/11] iomap: Handle tail pages in iomap_page_mkwrite Matthew Wilcox (Oracle)
2020-08-25 10:29 ` [PATCH 00/11] iomap/fs/block patches for 5.11 William Kucharski
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