On Thu, 2019-10-03 at 14:35 +0300, Jarkko Sakkinen wrote: > On Wed, Oct 02, 2019 at 08:41:45AM -0400, Mimi Zohar wrote: > > On Fri, 2019-09-27 at 16:06 +0300, Jarkko Sakkinen wrote: > > > On Wed, Sep 25, 2019 at 10:03:46AM -0400, James Bottomley wrote: > > > > On Wed, 2019-09-25 at 16:48 +0300, Jarkko Sakkinen wrote: > > > > [...] > > > > > + data_page = alloc_page(GFP_HIGHUSER); > > > > > + if (!data_page) > > > > > + return -ENOMEM; > > > > > + > > > > > + data_ptr = kmap(data_page); > > > > > > > > I don't think this is such a good idea. On 64 bit it's no different > > > > from GFP_KERNEL and on 32 bit where we do have highmem, kmap space is > > > > at a premium, so doing a highmem allocation + kmap is more wasteful of > > > > resources than simply doing GFP_KERNEL. In general, you should only do > > > > GFP_HIGHMEM if the page is going to be mostly used by userspace, which > > > > really isn't the case here. > > > > > > Changing that in this commit would be wrong even if you are right. > > > After this commit has been applied it is somewhat easier to make > > > best choices for allocation in each call site (probably most will > > > end up using stack). > > > > Agreed, but it could be a separate patch, prior to this one. Why > > duplicate the problem all over only to change it later? > > What problem exactly it is duplicating? The existing allocation > scheme here works correctly. In the current code "alloc_page(GFP_HIGHUSER)" exists in a single function. With this patch, "alloc_page(GFP_HIGHUSER)" is duplicated 24 times. If it is incorrect and we shouldn't be using GFP_HIGHUSER, as James said, then why duplicate it 24 times? Fix it as a separate patch first, that could be backported if needed, and then make the change. Mimi
