[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH v18 05/10] xbitmap: add more operations

From: Tetsuo Handa
Subject: Re: [Qemu-devel] [PATCH v18 05/10] xbitmap: add more operations
Date: Thu, 30 Nov 2017 22:35:03 +0900

Tetsuo Handa wrote:
> > +
> > +                   if (ebit >= BITS_PER_LONG)
> > +                           continue;
> (I don't understand how radix tree works, but generally this patchset looks 
> fuzzy
> to me about boundary cases. Thus, I want to confirm that this is not an 
> overlook.)
> Why is making "ebit >= BITS_PER_LONG" (e.g. start == 62) case a no-op correct?
> Aren't there bits which should have been cleared in this case?

According to xb_set_bit(), it seems to me that we are trying to avoid memory 
for "struct ida_bitmap" when all set bits within a 1024-bits bitmap reside in 
the first
61 bits.

But does such saving help? Is there characteristic bias that majority of set 
bits resides
in the first 61 bits, for "bit" is "unsigned long" which holds a page number 
(isn't it)?
If no such bias, wouldn't eliminating radix_tree_exception() case and always 
"struct ida_bitmap" simplifies the code (and make the processing faster)?

reply via email to

[Prev in Thread] Current Thread [Next in Thread]