commit 3fd2c26569a69d2c0cfd9303a60838bc8130eaff
author Jarryd <jarrydg@chromium.org> Wed Sep 16 06:31:55 2020
committer Commit Bot <commit-bot@chromium.org> Wed Sep 16 06:31:55 2020
tree 59092b519c979b634fd8f4aec2ecfdfab7c94869
parent fdc59761fa658f64f7689c60261826597eadf80b

Quota: Fix precision mistakes for storage pressure.

There have been a number of reports about the storage pressure
notification being shown, even when there is an absence of
storage pressure.

This is due to a numerical precision issue, where division of two
ints would almost always return 0. This 0 meant that a condition
that checked for storage pressure would always pass, and QuotaManger
would fire storage pressure notifications for all write errors,
regardless of disk availability.

This change removes the division operation entirely with a little
trick:

 - Given percent_available = 100 * available_space / total,
 - percent_available < kStoragePressureThresholdRatio  is equivalent
     to (substitution):
 - 100 * available_space / total < kStoragePressureThresholdRatio
     is equivalent to (multiply both sides by total):
 - 100 * available_space < kStoragePressureThresholdRatio * total

TBR=pwnall@chromium.org

Bug: 1127237
Change-Id: I79c5ff47f27824d25ff8e47dc4aed859c8d3cd7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412758
Reviewed-by: Jarryd Goodman <jarrydg@chromium.org>
Commit-Queue: Jarryd Goodman <jarrydg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807356}