Zach Brown c4663ea1a1 scoutfs: compact items in item cache pages ...

The first pass of the item cache didn't try to reclaim freed space at
all.  It would leave behind very sparse pages.  The oldest of which
would be reclaimed by memory pressure.

While this worked, it created much more stress on the system than is
necessary.  Splitting a page with one key also makes it hard to
calculate the boundaries of the split pages, given that the start and
end keys could be the single item.

This adds a header field which tracks the free space in item cache
pgaes.  Free space is created before the alloc offset by removing items
from the rbtree, but also from shrinking item values when updating or
deleting items.

If we try to split a page with sufficient free space to insert the
largest possible item then we compact the page instead of splitting it.
We copy the items into the front of an unused page and swap the pages.

Signed-off-by: Zach Brown <zab@versity.com>

2020-10-26 15:19:03 -07:00

kmod

scoutfs: compact items in item cache pages

2020-10-26 15:19:03 -07:00

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