On 14.03.23 10:48, Matthew Wilcox wrote:
On Tue, Mar 14, 2023 at 10:16:09AM +0100, David Hildenbrand wrote:
On 14.03.23 04:09, Yin Fengwei wrote:
For long term with wider adoption of large folio in kernel (like large
folio for anonymous page), MADV_PAGEOUT needs be updated to handle
large folio as whole to avoid splitting it always.
Just curious what the last sentence implies. Large folios are supposed to be
a transparent optimization. So why should we pageout all surrounding
subpages simply because a single subpage was requested to be paged out? That
might harm performance of some workloads ... more than the actual split.
So it's not immediately obvious to me why "avoid splitting" is the correct
answer to the problem at hand.
Even if your madvise() call says to pageout all pages covered by a
folio, the current code will split it. That's what needs to be fixed.
Agreed, if possible in the future (swap handling ...).
At least for anonymous pages, using large folios is an attempt to treat
all pages in a particular range the same way. If the user says to only
page out some of them, that's a big clue that these pages are different
from the other pages, and so we should split a folio where the madvise
call does not cover every page in the folio.
Agreed.
--
Thanks,
David / dhildenb
