Re: [Xen-devel] [PATCH v3 5/9] mm: Do not discard already-scrubbed pages if softirqs are pending

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.04.17 at 17:37, <boris.ostrovsky@xxxxxxxxxx> wrote:
> While scrubbing from idle loop, check for softirqs every 256 pages.
> If softirq is pending, don't scrub any further and merge the
> partially-scrubbed buddy back into heap by breaking the clean portion
> into smaller power-of-2 chunks. Then repeat the same process for the
> dirty part.

This is ugly, as it gets us back into the state where full merge
opportunities aren't being realized, just that the time window
may be smaller now. As hinted at before, is there no way to
flag the first page needing scrubbing alongside the head
indicating that _some_ page needs scrubbing? The pages are
all free, so if there's no other suitable storage, the head page
itself could serve as such. But instead of a flag in struct
page_info, perhaps you could store a (relatively small) integer?

Jan


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