Messages in this thread | | | Date | Fri, 10 Dec 2021 22:35:37 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/1] mm: bdi: Initialize bdi_min_ratio when bdi unregister |
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On Fri, Oct 22, 2021 at 03:58:13AM +0100, Matthew Wilcox wrote: > On Thu, Oct 21, 2021 at 07:45:30PM -0700, Andrew Morton wrote: > > On Thu, 21 Oct 2021 13:01:30 +0100 Matthew Wilcox <willy@infradead.org> wrote: > > > > > On Thu, Oct 21, 2021 at 04:16:52AM -0700, Christoph Hellwig wrote: > > > > On Fri, Oct 22, 2021 at 01:19:43AM +0900, Manjong Lee wrote: > > > > > Because when sdcard is removed, bdi_min_ratio value will remain. > > > > > Currently, the only way to reset bdi_ min_ratio is to reboot. > > > > > > > > But bdis that are unregistered are never re-registered. What is > > > > the problem you're trying to solve? > > > > > > The global bdi_min_ratio needs to be adjusted. See > > > bdi_set_min_ratio() in mm/page-writeback.c. > > > > I added cc:stable to this and tweaked the comment & coding style a bit: > > Definitely improvements on that front. > > I don't know the BDI code particularly well, and the implementation of > bdi_set_min_ratio() confuses me, so I can't say whether the original > patch is clearly correct or not.
Looks like something I might've written :-)
I'm thinking the part:
min_ratio -= bdi->min_ratio; if (bdi_min_ratio + min_ratio < 100) { bdi_min_ratio += min_ratio; bdi->min_ratio += min_ratio; }
is what confuses? particularly when min_ratio < bdi->min_ratio?
Anyway, two cases: bdi->min_ratio < min_ratio and bdi->min_ratio > min_ratio, let's do both with 0 and 10.
bdi->min_ratio = 0, min_ratio = 10 gives us:
min_ratio -= bdi->min_ratio; // 10 -= 0 == 10 if (bdi_min_ratio + min_ratio < 100) { // x + 10 < 100 bdi_min_ratio += min_ratio; // x += 10 bdi->min_ratio += min_ratio // 0 += 10 == 10 }
The other way around, bdi->min_raito = 10, min_ratio = 0:
min_ratio -= bdi->min_ratio; // 0 -= 10 == -10 if (bdi_min_ratio + min_ratio < 100) { // x + -10 < 100 bdi_min_ratio += min_ratio; // x += -10 bdi->min_ratio += min_ratio; // 10 += -10 == 0 }
Makes sense?
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