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From: Matthew Wilcox <willy@infradead.org>
To: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 20/51] block: Add bio_for_each_thp_segment_all
Date: Thu, 11 Jun 2020 11:20:29 -0700	[thread overview]
Message-ID: <20200611182029.GC8681@bombadil.infradead.org> (raw)
In-Reply-To: <20200610201345.13273-21-willy@infradead.org>

On Wed, Jun 10, 2020 at 01:13:14PM -0700, Matthew Wilcox wrote:
> +static inline void bvec_thp_advance(const struct bio_vec *bvec,
> +				struct bvec_iter_all *iter_all)
> +{
> +	struct bio_vec *bv = &iter_all->bv;
> +	unsigned int page_size = thp_size(bvec->bv_page);
> +
> +	if (iter_all->done) {
> +		bv->bv_page += thp_nr_pages(bv->bv_page);
> +		bv->bv_offset = 0;
> +	} else {
> +		BUG_ON(bvec->bv_offset >= page_size);
> +		bv->bv_page = bvec->bv_page;
> +		bv->bv_offset = bvec->bv_offset & (page_size - 1);
> +	}
> +	bv->bv_len = min(page_size - bv->bv_offset,
> +			 bvec->bv_len - iter_all->done);
> +	iter_all->done += bv->bv_len;
> +
> +	if (iter_all->done == bvec->bv_len) {
> +		iter_all->idx++;
> +		iter_all->done = 0;
> +	}
> +}

If, for example, we have an order-2 page followed by two order-0 pages
(thanks, generic/127!) in the bvec, we'll end up skipping the third
page because we calculate the size based on bvec->bv_page instead of
bv->bv_page.

+++ b/include/linux/bvec.h
@@ -166,15 +166,19 @@ static inline void bvec_thp_advance(const struct bio_vec *bvec,
                                struct bvec_iter_all *iter_all)
 {
        struct bio_vec *bv = &iter_all->bv;
-       unsigned int page_size = thp_size(bvec->bv_page);
+       unsigned int page_size;
 
        if (iter_all->done) {
                bv->bv_page += thp_nr_pages(bv->bv_page);
+               page_size = thp_size(bv->bv_page);
                bv->bv_offset = 0;
        } else {
-               BUG_ON(bvec->bv_offset >= page_size);
-               bv->bv_page = bvec->bv_page;
-               bv->bv_offset = bvec->bv_offset & (page_size - 1);
+               bv->bv_page = thp_head(bvec->bv_page +
+                               (bvec->bv_offset >> PAGE_SHIFT));
+               page_size = thp_size(bv->bv_page);
+               bv->bv_offset = bvec->bv_offset -
+                               (bv->bv_page - bvec->bv_page) * PAGE_SIZE;
+               BUG_ON(bv->bv_offset >= page_size);
        }
        bv->bv_len = min(page_size - bv->bv_offset,
                         bvec->bv_len - iter_all->done);

The previous code also wasn't handling the case fixed in 6bedf00e55e5
where a split bio might end up splitting a bvec.  That BUG_ON can probably
come out after a few months of testing.

  reply	other threads:[~2020-06-11 18:20 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-10 20:12 [RFC v6 00/51] Large pages in the page cache Matthew Wilcox
2020-06-10 20:12 ` [PATCH v6 01/51] mm: Print head flags in dump_page Matthew Wilcox
2020-06-10 20:12 ` [PATCH v6 02/51] mm: Print the inode number " Matthew Wilcox
2020-06-10 20:12 ` [PATCH v6 03/51] mm: Print hashed address of struct page Matthew Wilcox
2020-06-10 20:12 ` [PATCH v6 04/51] mm: Move PageDoubleMap bit Matthew Wilcox
2020-06-11 15:03   ` Zi Yan
2020-06-10 20:12 ` [PATCH v6 05/51] mm: Simplify PageDoubleMap with PF_SECOND policy Matthew Wilcox
2020-06-11 15:14   ` Zi Yan
2020-06-10 20:13 ` [PATCH v6 06/51] mm: Store compound_nr as well as compound_order Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 07/51] mm: Move page-flags include to top of file Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 08/51] mm: Add thp_order Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 09/51] mm: Add thp_size Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 10/51] mm: Replace hpage_nr_pages with thp_nr_pages Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 11/51] mm: Add thp_head Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 12/51] mm: Introduce offset_in_thp Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 13/51] mm: Support arbitrary THP sizes Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 14/51] fs: Add a filesystem flag for THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 15/51] fs: Do not update nr_thps for mappings which support THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 16/51] fs: Introduce i_blocks_per_page Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 17/51] fs: Make page_mkwrite_check_truncate thp-aware Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 18/51] mm: Support THPs in zero_user_segments Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 19/51] mm: Zero the head page, not the tail page Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 20/51] block: Add bio_for_each_thp_segment_all Matthew Wilcox
2020-06-11 18:20   ` Matthew Wilcox [this message]
2020-06-10 20:13 ` [PATCH v6 21/51] block: Support THPs in page_is_mergeable Matthew Wilcox
2020-06-12 16:17   ` Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 22/51] iomap: Support arbitrarily many blocks per page Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 23/51] iomap: Support THPs in iomap_adjust_read_range Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 24/51] iomap: Support THPs in invalidatepage Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 25/51] iomap: Support THPs in read paths Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 26/51] iomap: Convert iomap_write_end types Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 27/51] iomap: Change calling convention for zeroing Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 28/51] iomap: Change iomap_write_begin calling convention Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 29/51] iomap: Support THPs in write paths Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 30/51] iomap: Inline data shouldn't see THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 31/51] iomap: Handle tail pages in iomap_page_mkwrite Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 32/51] xfs: Support THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 33/51] mm: Make prep_transhuge_page return its argument Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 34/51] mm: Add __page_cache_alloc_order Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 35/51] mm: Allow THPs to be added to the page cache Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 36/51] mm: Allow THPs to be removed from " Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 37/51] mm: Remove page fault assumption of compound page size Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 38/51] mm: Fix total_mapcount assumption of " Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 39/51] mm: Remove assumptions of THP size Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 40/51] mm: Avoid splitting THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 41/51] mm: Fix truncation for pages of arbitrary size Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 42/51] mm: Handle truncates that split THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 43/51] mm: Support storing shadow entries for THPs Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 44/51] mm: Support retrieving tail pages from the page cache Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 45/51] mm: Support tail pages in wait_for_stable_page Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 46/51] mm: Add DEFINE_READAHEAD Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 47/51] mm: Make page_cache_readahead_unbounded take a readahead_control Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 48/51] mm: Make __do_page_cache_readahead " Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 49/51] mm: Allow PageReadahead to be set on head pages Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 50/51] mm: Add THP readahead Matthew Wilcox
2020-06-10 20:13 ` [PATCH v6 51/51] mm: Align THP mappings for non-DAX Matthew Wilcox
2020-06-11  6:59 ` [RFC v6 00/51] Large pages in the page cache Christoph Hellwig
2020-06-11 11:24   ` Matthew Wilcox
2020-06-15 13:32     ` Christoph Hellwig
2020-06-14 16:26 ` Matthew Wilcox

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