Date: Thu, 07 Oct 2010 20:16:16 +0300 From: Andriy Gapon <avg@freebsd.org> To: freebsd-current@freebsd.org Cc: Alan Cox <alc@freebsd.org>, Garrett Cooper <yanefbsd@gmail.com>, Alan Cox <alc@rice.edu> Subject: Re: minidump size on amd64 Message-ID: <4CAE0060.7050607@freebsd.org> In-Reply-To: <4CA5911E.3000101@freebsd.org> References: <4CA0DA49.2090006@freebsd.org> <4CA3A48A.5070300@freebsd.org> <4CA3BD1E.5070807@rice.edu> <4CA5911E.3000101@freebsd.org>
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on 01/10/2010 10:43 Andriy Gapon said the following: > The idea. We dump contiguously only pages with PDEs (which means both valid and > invalid PDEs), valid pages with PTEs are dumped the same way as data physical > pages (i.e. via dump_add_page, etc); no fake PTEs for 2MB pages. > PDE area of the dump takes about 20MB as opposed to 1GB for PTE area (the math > is obvious, but just in case). > > libkva is changed to treat former PTE area as PDE area and is also taught to > understand PG_PS in PDE. > There is now an overhead of having to first read a PTE page in V-to-P-to-offset > lookup for !PG_PS case. Perhaps we could cache all PTEs in memory and have a > lookup table for them, but I didn't bother with this possibly premature > optimization at this time. > > There is an unrelated change in minidumpsys - "bitmap_frozen". > I had to do it despite having a patch in my local tree to stop other CPUs on > panic->dump. Code in dump path (peripheral disk driver, CAM, SIM driver, > something else?) seems to do some memory allocations and change dump bitmap, > which leads to a mismatch between dump size and dump bitmap; and also > potentially to inconsistencies in the bitmap itself. So I decided that it's a > good idea to freeze the bitmap once we decided what pages we want to dump. > > Some variables and structure fields with 'pte' in them should probably be > renamed to have 'pde' instead. Here's an updated patch: http://people.freebsd.org/~avg/amd64-minidump.3.diff I went ahead and changed 'pte' to 'pde' in various names. Also, I ditched somewhat questionable "bitmap_frozen" approach and instead opted for restarting a dump on a size mismatch. This was suggested by kib@. Garret Cooper has pointed out some problems with bitmap_frozen approach. I think that actual problem was a scenario where a dump is done, then the system is allowed to continue and then another dump is done. An exotic case perhaps? :-) One probably desirable feature that is missing is backward compatibility in libkvm. If that is a showstopper, then I'll have to work on preserving it. As usual, I will appreciate any feedback - reviews, testing, etc. Thanks! -- Andriy Gapon
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