Messages in this thread | | | Date | Thu, 21 May 2020 17:04:11 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH v4 00/36] Large pages in the page cache |
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On Fri, May 22, 2020 at 08:49:06AM +1000, Dave Chinner wrote: > Ok, so the main issue I have with the filesystem/iomap side of > things is that it appears to be adding "transparent huge page" > awareness to the filesysetm code, not "large page support". > > For people that aren't aware of the difference between the > transparent huge and and a normal compound page (e.g. I have no idea > what the difference is), this is likely to cause problems, > especially as you haven't explained at all in this description why > transparent huge pages are being used rather than bog standard > compound pages.
The primary reason to use a different name from compound_* is so that it can be compiled out for systems that don't enable CONFIG_TRANSPARENT_HUGEPAGE. So THPs are compound pages, as they always have been, but for a filesystem, using thp_size() will compile to either page_size() or PAGE_SIZE depending on CONFIG_TRANSPARENT_HUGEPAGE.
Now, maybe thp_size() is the wrong name, but then you need to suggest a better name ;-)
> And, really, why should iomap or the filesystems care if the large > page is a THP or just a high order compound page? The interface > for operating on these things at the page cache level should be the > same. We already have page_size() and friends for operating on > high order compound pages, yet the iomap stuff has this new > thp_size() function instead of just using page_size(). THis is going > to lead to confusion and future bugs when people who don't know the > difference use the wrong page size function in their filesystem > code.
There is no wrong function to use -- just one that expands to more code in the case where CONFIG_TRANSPARENT_HUGEPAGE is disabled.
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