Messages in this thread | | | Date | Thu, 15 Jul 2021 23:20:17 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH v14 124/138] fs: Convert vfs_dedupe_file_range_compare to folios |
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On Thu, Jul 15, 2021 at 03:08:40PM -0700, Darrick J. Wong wrote: > On Thu, Jul 15, 2021 at 04:36:50AM +0100, Matthew Wilcox (Oracle) wrote: > > We still only operate on a single page of data at a time due to using > > kmap(). A more complex implementation would work on each page in a folio, > > but it's not clear that such a complex implementation would be worthwhile. > > Does this break up a compound folio into smaller pages?
No. We just operate on each page in turn. Splitting a folio is an expensive and unrealiable thing to do, so we avoid it unless necessary.
> > +/* Unlock two folios, being careful not to unlock the same folio twice. */ > > +static void vfs_unlock_two_folios(struct folio *folio1, struct folio *folio2) > > { > > - unlock_page(page1); > > - if (page1 != page2) > > - unlock_page(page2); > > + folio_unlock(folio1); > > + if (folio1 != folio2) > > + folio_unlock(folio2); > > This could result in a lot of folio lock cycling. Do you think it's > worth the effort to minimize this by keeping the folio locked if the > next page is going to be from the same one?
I think that might well be a worthwhile optimisation. I'd like to do that as a separate patch, though (and maybe somebody other than me could do it ;-)
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