On 04/06/2024 7:27, Christoph Hellwig wrote:
On Tue, Jun 04, 2024 at 12:27:06AM +0300, Sagi Grimberg wrote:
I still don't understand how a page in the middle of a contiguous range ends
up coming from the slab while others don't.
I haven't investigate the origin of the IO
yet. I suspect the first 2 pages are the superblocks of the raid
(mdp_superblock_1 and bitmap_super_s) and the rest of the IO is the bitmap.
Well, if these indeed are different origins and just *happen* to be a
mixture
of slab originated pages and non-slab pages combined together in a single
bio of a bvec entry,
I'd suspect that it would be more beneficial to split the bvec (essentially
not allow bio_add_page
to append the page to tail bvec depending on a queue limit (similar to how
we handle sg gaps).
So you want to add a PageSlab check to bvec_try_merge_page? That sounds
fairly expensive..
The check needs to happen somewhere apparently, and given that it will
be gated by a queue flag
only request queues that actually needed will suffer, but they will
suffer anyways...
