| Message ID | 20211021161942.5983-1-mj0123.lee@samsung.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1] mm: bdi: Initialize bdi_min_ratio when bdi unregister | expand |
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?
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.
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: --- a/mm/backing-dev.c~mm-bdi-initialize-bdi_min_ratio-when-bdi-unregister-fix +++ a/mm/backing-dev.c @@ -947,10 +947,12 @@ void bdi_unregister(struct backing_dev_i wb_shutdown(&bdi->wb); cgwb_bdi_unregister(bdi); - /* if min ratio doesn't 0, it has to set 0 before unregister */ - if (bdi->min_ratio) { + /* + * If this BDI's min ratio has been set, use bdi_set_min_ratio() to + * update the global bdi_min_ratio. + */ + if (bdi->min_ratio) bdi_set_min_ratio(bdi, 0); - } if (bdi->dev) { bdi_debug_unregister(bdi);
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.
>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. Thank Andrew Morton for modifying the comment & style. :) Dear Matthew Wilcox. Please tell me about it more? I want to know more, and I want to find a way to improve it. :)
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?
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: Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- a/mm/backing-dev.c~mm-bdi-initialize-bdi_min_ratio-when-bdi-unregister-fix > +++ a/mm/backing-dev.c > @@ -947,10 +947,12 @@ void bdi_unregister(struct backing_dev_i > wb_shutdown(&bdi->wb); > cgwb_bdi_unregister(bdi); > > - /* if min ratio doesn't 0, it has to set 0 before unregister */ > - if (bdi->min_ratio) { > + /* > + * If this BDI's min ratio has been set, use bdi_set_min_ratio() to > + * update the global bdi_min_ratio. > + */ > + if (bdi->min_ratio) > bdi_set_min_ratio(bdi, 0); > - } > > if (bdi->dev) { > bdi_debug_unregister(bdi); > _ >
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 4a9d4e27d0d9..ca53807be188 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -947,6 +947,11 @@ void bdi_unregister(struct backing_dev_info *bdi) wb_shutdown(&bdi->wb); cgwb_bdi_unregister(bdi); + /* if min ratio doesn't 0, it has to set 0 before unregister */ + if (bdi->min_ratio) { + bdi_set_min_ratio(bdi, 0); + } + if (bdi->dev) { bdi_debug_unregister(bdi); device_unregister(bdi->dev);
Initialize min_ratio if it is set when bdi unregister. It can prevent problems that may occur when bdi is removed without resetting min_ratio. For example. 1) insert external sdcard 2) set external sdcard's min_ratio 70 3) remove external sdcard without setting min_ratio 0 4) insert external sdcard 5) set external sdcard's min_ratio 70 << error occur(can't set) Because when sdcard is removed, bdi_min_ratio value will remain. Currently, the only way to reset bdi_ min_ratio is to reboot. Signed-off-by: Manjong Lee <mj0123.lee@samsung.com> --- mm/backing-dev.c | 5 +++++ 1 file changed, 5 insertions(+)