On 2014/01/10 7:23:32, crash-utility-bounces@xxxxxxxxxx wrote: > On Thu, Jan 09, 2014 at 04:11:40PM -0500, Dave Anderson wrote: > > > > > > > Version 2 > > > > > > > - Moves the warning to this point: > > > > > > > ... > > > > > > > This GDB was configured as "x86_64-unknown-linux-gnu"... > > > > > > > > > > > > > > WARNING: All unused vmemmap page structures are excluded from > > > > > > > this > > > > > > > dump. > > > > > > > This will cause failures of the kmem command if it > > > > > > > attempts to > > > > > > > walk any list of free pages (with options -f -F -i -s > > > > > > > and > > > > > > > -S). > > > > > > > > > > > > > > SYSTEM MAP: /boot/System.map-2.6.32-cpw > > > > > > > ... > > > > > > > > > > > > > > - Drop patch 2, which added warnings to individual kmem options. > > > > > > > > > > > > > > - Feel free to change the wording of the warning. > > > > > > > > > > > > > > And this patch is contingent upon the acceptance of a change to the > > > > > > > makedumpfile command. > > > > > > > http://marc.info/?l=kexec&m=138853299130125&w=2 > > > > > > > > > > > > > > > > > > > > > If makedumpfile excludes unused page structures it will flag that > > > > > > > fact in the dump header. > > > > > > > (There are about 3.67 million pages full of page structures for > > > > > > > every tera byte of system memory. The great bulk of those > > > > > > > page structures are not needed.) > > > > > > > Their exclusion is a makedumpfile option. > > > > > > > > > > > > > > Crash will display a note during initialization if such structures > > > > > > > have been excluded. Crash commands that walk page freelists, for > > > > > > > example, will fail. So the note will help the user understand why. > > > > > > > > > > > > > > Signed-off-by: Cliff Wickman <cpw@xxxxxxx> > > > > > > > --- > > > > > > > defs.h | 1 + > > > > > > > diskdump.c | 3 +++ > > > > > > > diskdump.h | 1 + > > > > > > > main.c | 6 ++++++ > > > > > > > 4 files changed, 11 insertions(+) > > > > > > > > > > > > > > Index: crash-7.0.4/diskdump.c > > > > > > > =================================================================== > > > > > > > --- crash-7.0.4.orig/diskdump.c > > > > > > > +++ crash-7.0.4/diskdump.c > > > > > > > @@ -749,6 +749,9 @@ restart: > > > > > > > dd->valid_pages[i]++; > > > > > > > } > > > > > > > > > > > > > > + if (header->status & DUMP_DH_EXCLUDED_VMEMMAP) > > > > > > > + pc->flags2 |= VMEXCLUDED; > > > > > > > + > > > > > > > return TRUE; > > > > > > > > > > > > > > err: > > > > > > > Index: crash-7.0.4/diskdump.h > > > > > > > =================================================================== > > > > > > > --- crash-7.0.4.orig/diskdump.h > > > > > > > +++ crash-7.0.4/diskdump.h > > > > > > > @@ -84,6 +84,7 @@ struct kdump_sub_header { > > > > > > > #define DUMP_DH_COMPRESSED_ZLIB 0x1 /* page is compressed with > > > > > > > zlib > > > > > > > */ > > > > > > > #define DUMP_DH_COMPRESSED_LZO 0x2 /* page is compressed with > > > > > > > lzo > > > > > > > */ > > > > > > > #define DUMP_DH_COMPRESSED_SNAPPY 0x4 /* page is compressed with > > > > > > > snappy > > > > > > > */ > > > > > > > +#define DUMP_DH_EXCLUDED_VMEMMAP 0x8 /* unused vmemmap pages are > > > > > > > excluded */ > > > > > > > > > > > > > > /* descriptor of each page for vmcore */ > > > > > > > typedef struct page_desc { > > > > > > > Index: crash-7.0.4/defs.h > > > > > > > =================================================================== > > > > > > > --- crash-7.0.4.orig/defs.h > > > > > > > +++ crash-7.0.4/defs.h > > > > > > > @@ -505,6 +505,7 @@ struct program_context { > > > > > > > #define VMCOREINFO (0x400ULL) > > > > > > > #define ALLOW_FP (0x800ULL) > > > > > > > #define REM_PAUSED_F (0x1000ULL) > > > > > > > +#define VMEXCLUDED (0x2000ULL) > > > > > > > #define REMOTE_PAUSED() (pc->flags2 & REM_PAUSED_F) > > > > > > > char *cleanup; > > > > > > > char *namelist_orig; > > > > > > > Index: crash-7.0.4/main.c > > > > > > > =================================================================== > > > > > > > --- crash-7.0.4.orig/main.c > > > > > > > +++ crash-7.0.4/main.c > > > > > > > @@ -662,6 +662,12 @@ main_loop(void) > > > > > > > } else > > > > > > > SIGACTION(SIGINT, restart, &pc->sigaction, NULL); > > > > > > > > > > > > > > + if (pc->flags2 & VMEXCLUDED) > > > > > > > + fprintf(fp, > > > > > > > + "WARNING: All unused vmemmap page structures are excluded > > > > > > > from > > > > > > > this dump.\n" > > > > > > > + " This will cause failures of the kmem command if it > > > > > > > attempts > > > > > > > to\n" > > > > > > > + " walk any list of free pages (with options -f -F -i -s and > > > > > > > -S).\n\n"); > > > > > > > + > > > > > > > /* > > > > > > > * Display system statistics and current context. > > > > > > > */ > > > > > > > > > > > > > > > > > > > This patch looks reasonable. > > > > > > > > > > > > BTW, what happens if you enter "kmem <address>" alone with no option? > > > > > > It should fail as well, no? > > > > > > > > > > Yes, it does. > > > > > > > > > > crash> kmem 133360 > > > > > kmem: page excluded: kernel virtual address: ffffea0000004350 type: > > > > > "page.lru.next" > > > > > > > > > > crash> kmem ffff8897baae7540 > > > > > CACHE NAME OBJSIZE ALLOCATED TOTAL SLABS > > > > > SSIZE > > > > > ffff88c7bec70040 task_struct 2656 4578 5361 1787 > > > > > 8k > > > > > SLAB MEMORY TOTAL ALLOCATED FREE > > > > > ffff8897baae6040 ffff8897baae6080 3 2 1 > > > > > FREE / [ALLOCATED] > > > > > [ffff8897baae7540] > > > > > > > > > > kmem: page excluded: kernel virtual address: ffffea0000007028 type: "first list entry" > > > > > > > > > > Another way to search a freelist, that I didn't notice. > > > > > Do you want to add that to the warning? > > > > > > > > I'm thinking that there might be others as well. Like how does "kmem -p" handle > > > > the missing page structs? > > > > > > kmem -p gives the appearance of working, but is unable to read the > > > mem_map pages. It is giving false results. > > > This is an example of what you feared. > > > > > > If we do this: > > > > > > --- > > > memory.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > Index: crash-7.0.4/memory.c > > > =================================================================== > > > --- crash-7.0.4.orig/memory.c > > > +++ crash-7.0.4/memory.c > > > @@ -5657,7 +5657,7 @@ fill_mem_map_cache(ulong pp, ulong ppend > > > * Try to read it in one fell swoop. > > > */ > > > if (readmem(pp, KVADDR, page_cache, SIZE(page) * PGMM_CACHED, > > > - "page struct cache", RETURN_ON_ERROR|QUIET)) > > > + "page struct cache", FAULT_ON_ERROR)) > > > return; > > > > > > /* > > > > > > Then we see the immediate failure: > > > > > > crash> kmem -p > > > PAGE PHYSICAL MAPPING INDEX CNT FLAGS > > > kmem: page excluded: kernel virtual address: ffffea0000004000 type: "page > > > struct cache" > > > > > > What should be done about that? > > > > I'd leave it alone -- at least it doesn't fail miserably like the other commands. > > > > > I wonder why the reads of the mem_map were done with RETURN_ON_ERROR|QUIET > > > to begin with? > > > > It's done to guard against a vmemmap boundary (real page structs vs. unmapped > > page structs) that happens to occur within the 512-page-size chunk of memory > > that's being cached. So first it tries to read the full chunk in one readmem(), > > but if that fails, it breaks up the read requests, zeroing out the unmapped pages. > > > > Dave > > Okay. I'll just make issue a more general warning like: > > WARNING: All unused vmemmap page structures are excluded from this dump. > This will cause failures in any command that accesses page > structures of pages that are not included in the dump. This > is particularly likely when using several options of the > kmem command. > > If that looks reasonable to you. Dave, the excluding vmemmap obviously affect a user's investigation, is this really acceptable for you ? There is no chance to re-capture the same dump image, I think we should be more carefully about filtering out since it's an irreversible change. How many users want to get such a broken dump image even if it could be gotten faster ? Why we capture dump images, it's for analyzing, of course. At least, we should supply alternatives to the affected commands. Thanks Atsushi Kumagai > -Cliff > > > > > > > > -Cliff > > > > > > > > > > > It might be better to just generally warn that results may be unpredictable > > > > because any command that accesses page structures, such as kmem, may fail. > > > > By listing specific options, it makes it sound like that they are the only > > > > ones, so it may be better to leave it open-ended. > > > > > > > > Dave > > > > > > -- > > > Cliff Wickman > > > SGI > > > cpw@xxxxxxx > > > (651) 683-3824 > > > > > -- > Cliff Wickman > SGI > cpw@xxxxxxx > (651) 683-3824 > > -- > Crash-utility mailing list > Crash-utility@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/crash-utility -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
