Messages in this thread | | | Date | Mon, 04 Apr 2011 09:05:16 -0700 | Subject | Re: [PATCH] MTD: Retry Read/Write Transfer Buffer Allocations | From | Grant Erickson <> |
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On 4/4/11 12:27 AM, Artem Bityutskiy wrote: > [CCing LKML in a hope to get good suggestions] > [The patch: > http://lists.infradead.org/pipermail/linux-mtd/2011-April/034645.html] > > Hi Grant, > > Just in case, Jarkko was trying to address the same issue recently: > > http://lists.infradead.org/pipermail/linux-mtd/2011-March/034416.html > > This should be a bit more complex I think. First of all, I think it is > better to make this a separate function. Second, you should make sure > the system does not print scary warnings when the allocation fails - use > __GFP_NOWARN flag, just like Jarkko did. > > An third, as I wrote in my answer to Jarkko, allocating large contiguous > buffers is bad for performance: if the system memory is fragmented and > there is no such large contiguous areas, the kernel will start writing > back dirty FS data, killing FS caches, shrinking caches and buggers, > probably even swapping out applications. We do not want MTD to cause > this at all. > > Probably we can mitigate this with kmalloc flags. Now, I'm not sure what > flags are the optimal, but I'd do: > > __GFP_NOWARN | __GFP_WAIT | __GFP_NORETRY > > May be even __GFP_WAIT flag could be kicked out.
Artem:
Thanks for the feedback and the link to Jarkko's very similar patch. Your suggestions will be incorporated into a subsequent patch.
For reference, I pursued a second uses-less-memory-but-is-more-complex approach that does get_user_pages, builds up a series of iovecs for the page extents. This worked well for all read cases I could test; however, for the write case, the approach required yet more refinement and overhead since the head and tail of the transfer need to be deblocked with read-modify-write due to the NOTALIGNED checks in nand_base.c:nand_do_write_ops. I am happy to share the work-in-progress with the list if anyone is interested.
I propose a two-stage approach. This issue has been in the kernel for about six years.
Can we take a modified version of Jarkko's or my simpler fixes for the first pass and then iterate toward the get_user_pages scatter/gather approach later?
Best,
Grant
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