As a start to getting back into Hurd hacking mode, I have begun to review your ext2fs patch for large file system support. At this point, I have only reviewed the libpager changes in any detail. I want to work with you to develop a well thought out interface and implementation that not only does the job but is elegant and represents something with which I feel comfortable in advocating acceptance into the mainline.
Great! Please use version 20040421 from http://debian.fmi.uni-sofia.bg/~ogi/hurd/ext3fs/ . It's not uploaded in Savannah and contains some major changes in the core function that remaps pages.
As such, I advise that we remove this extra flexibility and have pager_notify_pageout (which I prefer to call pager_notify_evict as data can be paged out without being evicted in the case of flushing dirty pages) called on a _per pager_ basis and indicate whether or not it should be called in the struct pager and set by pager_create. If it is useful, we may also have a pair of get and set methods to toggle it, however, the implementation of turning this feature on after a pager has been executing for some time seems problematic: all pages need to be marked as precious; I can't think of an easy way to do this off hand.
Yes, in ext2fs, we need either all or none pages to be marked as precious. I can't predict if there will be future pager users that will want more fine-grained marking, so I've just taken this by-page approach. In conclusion, I think it's OK this option to be pager-wide.
Second, Ognyan suggests that there is a race.
I wouldn't find it if I didn't experience it :-) BTW In complete hurd build, this optimization turns 1-3 times, usually 1 time.
My sense is that this problem can be easily avoided by not sending a pager_notify_pageout in data-return.c if PM_PAGEINWAIT is set thereby eliminating all of the hubbub with PM_FORCEREAD and the inefficiencies which is introduces. Or perhaps, I am missing some subtility.
This sounds reasonable. I need to think a bit more about it though.
Finally, when a pager_notify_evict is called on a page, the page is potentially changed. Hence any state associated with the page must also be changed. That is, its pagemap entry needs to be cleared otherwise, a page which is marked PM_EIO is shows for the wrong page.
Right, I didn't catch this. The error will be lost, but libpager can do nothing about it.
So what name should our pager-wide flag has? Following the current patch and the pager_notify_pageout -> pager_notify_evict rename, I will use notify_on_evict if noone has better proposal.
I'm close to releasing ext3fs 0.1, and after that I'll make these changes and future ones that will eventually come up.
Regards, ogi
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