Messages in this thread |  | | From | "Christian Ehrhardt" <> | Date | Mon, 26 Aug 2002 22:58:58 +0200 | Subject | Re: MM patches against 2.5.31 |
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On Mon, Aug 26, 2002 at 10:09:38PM +0200, Daniel Phillips wrote: > On Monday 26 August 2002 22:00, Christian Ehrhardt wrote: > > On Mon, Aug 26, 2002 at 07:56:52PM +0200, Daniel Phillips wrote: > > > On Monday 26 August 2002 17:29, Christian Ehrhardt wrote: > > > > On Mon, Aug 26, 2002 at 04:22:50PM +0200, Daniel Phillips wrote: > > > > > On Monday 26 August 2002 11:10, Christian Ehrhardt wrote: > > > > > > + * A special Problem is the lru lists. Presence on one of these lists > > > > > > + * does not increase the page count. > > > > > > > > > > Please remind me... why should it not? > > > > > > > > Pages that are only on the lru but not reference by anyone are of no > > > > use and we want to free them immediatly. If we leave them on the lru > > > > list with a page count of 1, someone else will have to walk the lru > > > > list and remove pages that are only on the lru. > > > > > > I don't understand this argument. Suppose lru list membership is worth a > > > page count of one. Then anyone who finds a page by way of the lru list can > > > > This does fix the double free problem but think of a typical anonymous > > page at exit. The page is on the lru list and there is one reference held > > by the pte. According to your scheme the pte reference would be freed > > (obviously due to the exit) but the page would remain on the lru list. > > However, there is no point in leaving the page on the lru list at all. > > If you want the page off the lru list at that point (which you probably do) > then you take the lru lock and put_page_testzero.
Could you clarify what you mean with "at that point"? Especially how do you plan to test for "this point". Besides it is illegal to use the page after put_page_testzero (unless put_page_testzero returns true).
> > If you think about who is going to remove the page from the lru you'll > > see the problem. > > Nope, still don't see it. Whoever hits put_page_testzero frees the page, > secure in the knowlege that there are no other references to it.
Well yes, but we cannot remove the page from the lru atomatically at page_cache_release time if we follow your proposal. If you think we can, show me your implementation of page_cache_release and I'll show you where the races are (unless you do everything under the lru_lock of course).
regards Christian
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