Date: Wed, 10 Nov 2010 12:45:00 -0600 From: Alan Cox <alc@rice.edu> To: Andriy Gapon <avg@freebsd.org> Cc: Alan Cox <alc@freebsd.org>, freebsd-current@freebsd.org Subject: Re: minidump size on amd64 Message-ID: <4CDAE82C.2040708@rice.edu> In-Reply-To: <4CD996AF.2070300@freebsd.org> References: <4CA0DA49.2090006@freebsd.org> <4CA3A48A.5070300@freebsd.org> <4CA3BD1E.5070807@rice.edu> <4CA5911E.3000101@freebsd.org> <4CAE0060.7050607@freebsd.org> <4CAECC4D.90707@rice.edu> <4CD1AA45.7000504@freebsd.org> <4CD1AD80.2090903@rice.edu> <4CD1D4AA.3060309@freebsd.org> <4CD8FFFF.3070106@rice.edu> <4CD996AF.2070300@freebsd.org>
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Andriy Gapon wrote:
> on 09/11/2010 10:02 Alan Cox said the following:
>
>> The kernel portion of the patch looks correct. If I were to make one stylistic
>> suggestion, it would be to make the control flow of the outer and inner loops as
>> similar as possible, that is,
>>
>> for (...
>> if ((pdp[i] & PG_V) == 0) {
>> ...
>> continue;
>> }
>> if ((pdp[i] & PG_PS) != 0) {
>> ...
>> continue;
>> }
>> for (...
>> if ((pd[j] & PG_V) == 0)
>> continue;
>> if ((pd[j] & PG_PS) != 0) {
>> ...
>> continue;
>> }
>> for (...
>> if ((pt[x] & PG_V) == 0)
>> continue;
>> ...
>>
>> I think this would make the code a little easier to follow.
>>
>
> This is a very nice suggestion, thank you.
> Besides the uniformity some horizontal space is saved too :-)
> Updated patch (only kernel part) is here:
> http://people.freebsd.org/~avg/amd64-minidump.5.diff
>
>
In the later loop, where you actually write the page directory pages,
the "va += ..." in the following looks like a bug because you also
update "va" in for (...):
+
+ /* 1GB page is represented as 512 2MB pages in a dump */
+ if ((pdp[i] & PG_PS) != 0) {
+ va += NBPDP;
My last three comments are:
1. I would move the assignment
i = (va >> PDPSHIFT) & ((1ul << NPDPEPGSHIFT) - 1);
so that it comes after
pmapsize += PAGE_SIZE;
2. The outermost ()'s aren't needed in the following statement:
j = ((va >> PDRSHIFT) & ((1ul << NPDEPGSHIFT) - 1));
3. I would suggest rewriting the following:
+ pa = pdp[i] & PG_PS_FRAME;
+ for (j = 0; j < NPDEPG; j++)
+ fakepd[j] = (pa + (j << PDRSHIFT)) |
+ PG_V | PG_PS | PG_RW | PG_A | PG_M;
fakepd[0] = pdp[i];
for (j = 1; j < NPDEPG; j++)
fakepd[j] = fakepd[j - 1] + NBPDR;
Then, whatever properties the pdp entry has will be inherited by the pd
entry.
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