Messages in this thread |  | | Subject | Re: [PATCH v2 1/1] block: blk-merge: don't merge the pages with non-contiguous descriptors | From | James Bottomley <> | Date | Thu, 17 Jan 2013 11:19:21 +0000 |
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On Thu, 2013-01-17 at 11:04 +0000, Russell King - ARM Linux wrote: > On Thu, Jan 17, 2013 at 11:01:47AM +0000, James Bottomley wrote: > > On Thu, 2013-01-17 at 10:47 +0000, Russell King - ARM Linux wrote: > > > Also, couldn't the addition of the scatterlist offset to the page also > > > be buggy too? > > > > No, fortunately, offset must be within the first page from the point of > > view of block generated sg lists. As long as nothing within arm > > violates this, it should be a safe assumption ... although the code > > seems to assume otherwise. > > Are you absolutely sure about that? I believe I have seen cases where > that has been violated in the past, though it was many years ago.
From the point of view of the block layer, absolutely: the scatterlist is generated from an array of bio_vecs. Each bio_vec is a page, offset and length element and obeys the rule that offset must be within the page and offset + length cannot stray over the page.
From the point of view of other arm stuff, I don't know.
James
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