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SubjectRe: [PATCH 2/4] KVM: Avoid checking huge page mappings in get_dirty_log()
Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> wrote:

> Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> wrote:
>
> > + while (mask) {
> > + rmapp = &slot->rmap[gfn_offset + __ffs(mask)];
> > + __rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);
> >
> > - return write_protected;
> > + /* clear the first set bit */
> > + mask &= mask - 1;
> > + }
> > }
>
> while (mask) {
> fsbit = __ffs(mask);
> gfn_offset += fsbit;
> mask >>= fsbit + 1;
>
> rmapp = &slot->rmap[gfn_offset];
> __rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);
> }
>
> Seems to be better: BSF friendly.

I was wrong.

"and < shift" and bsf did not show any difference for this kind of loop
on my box. So we should keep the original implementation.

Takuya


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