Re: CVS commit: [tls-maxphys] src/sys/dev

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Tue, Oct 09, 2012 at 05:59:06PM -0700, Chuck Silvers wrote:
> 
> if so, then the reason for the 64k writes would be this block of code in 
> ffs_write():
> 
>               if (!async && oldoff >> 16 != uio->uio_offset >> 16) {
>                       mutex_enter(vp->v_interlock);
>                       error = VOP_PUTPAGES(vp, (oldoff >> 16) << 16,
>                           (uio->uio_offset >> 16) << 16,
>                           PGO_CLEANIT | PGO_JOURNALLOCKED | PGO_LAZY);
>                       if (error)
>                               break;
>               }

Upon reflection, I do not understand how this works.

Consider a write() of 131072 starting at file offset 0.

oldoff >> 16 will be 0; uio->uio_offset will be 131072, unless
this is the source of my misunderstanding, after the call to ubc_uiomove().
Otherwise, I don't see how uio->uio_offset gets updated at all.

Now, we VOP_PUTPAGES(vp, 0, (131072 >> 16) << 16)) which is of course
VOP_PUTPAGES(vp, 0, 131072).  So why does this only push out 64K?

Thor