On Wed, 14 May 2008 11:40:30 +0400 Evgeniy Polyakov <johnpol@xxxxxxxxxxx> wrote: > Hi Andrew. > > On Tue, May 13, 2008 at 11:33:41PM -0700, Andrew Morton (akpm@xxxxxxxxxxxxxxxxxxxx) wrote: > > If any thread takes more than one kmap() at a time, it is deadlockable. > > Because there is a finite pool of kmaps. Everyone can end up holding > > one or more kmaps, then waiting for someone else to release one. > > It never takes the whole LAST_PKMAP maps. So the same can be applied to > any user who kmaps at least one page - while user waits for free slot, > it can be reused by someone else and so on. > > But it can be speed issue, on 32 bit machine with 8gb of ram essentially > all pages were highmem and required mapping, so this does slows things > down (probably a lot), so I will extend writeback path of the POHMELFS > not to kmap pages, but instead use ->sendpage(), which if needed will > map page one-by-one. Current approach when page is mapped and then > copied looks really beter since the only one sending function is used > which takes lock only single time. OK. > > Duplicating page_waitqueue() is bad. Exporting it is probably bad too. > > Better would be to help us work out why the core kernel infrastructure is > > unsuitable, then make it suitable. > > When ->writepage() is used, it has to wait until page is written (remote > side sent acknowledge), so if multiple pages are being written > simultaneously we either have to allocate shared structure or use > per-page wait. That sounds exactly like wait_on_page_writeback()? > Right now there are transactions (and they will be used > for all operations eventually), so this waiting can go away. > It is exactly the same logic which lock_page() uses. > > Will lock_page_killable()/__lock_page_killable() be exported to modules? Maybe, if there's a need. I see no particular problem with that. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
