lkml.org 
[lkml]   [2021]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v2 02/10] fsdax: Factor helper: dax_fault_actor()
    On Fri, Feb 26, 2021 at 08:20:22AM +0800, Shiyang Ruan wrote:
    > The core logic in the two dax page fault functions is similar. So, move
    > the logic into a common helper function. Also, to facilitate the
    > addition of new features, such as CoW, switch-case is no longer used to
    > handle different iomap types.
    >
    > Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
    > ---
    > fs/dax.c | 211 ++++++++++++++++++++++++++++++-------------------------
    > 1 file changed, 117 insertions(+), 94 deletions(-)
    >
    > diff --git a/fs/dax.c b/fs/dax.c
    > index 7031e4302b13..9dea1572868e 100644
    > --- a/fs/dax.c
    > +++ b/fs/dax.c
    > @@ -1289,6 +1289,93 @@ static int dax_fault_cow_page(struct vm_fault *vmf, struct iomap *iomap,
    > return 0;
    > }
    >
    > +static vm_fault_t dax_fault_insert_pfn(struct vm_fault *vmf, pfn_t pfn,
    > + bool pmd, bool write)
    > +{
    > + vm_fault_t ret;
    > +
    > + if (!pmd) {
    > + struct vm_area_struct *vma = vmf->vma;
    > + unsigned long address = vmf->address;
    > +
    > + if (write)
    > + ret = vmf_insert_mixed_mkwrite(vma, address, pfn);
    > + else
    > + ret = vmf_insert_mixed(vma, address, pfn);
    > + } else
    > + ret = vmf_insert_pfn_pmd(vmf, pfn, write);

    What about simplifying this a little bit more, something like:

    if (pmd)
    return vmf_insert_pfn_pmd(vmf, pfn, write);

    if (write)
    return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
    return vmf_insert_mixed(vmf->vma, vmf->address, pfn);

    also given that this only has a single user, why not keep open coding
    it in the caller?

    > +#ifdef CONFIG_FS_DAX_PMD
    > +static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
    > + struct iomap *iomap, void **entry);
    > +#else
    > +static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
    > + struct iomap *iomap, void **entry)
    > +{
    > + return VM_FAULT_FALLBACK;
    > +}
    > +#endif

    Can we try to avoid the forward declaration? Also is there a reason
    dax_pmd_load_hole does not compile for the !CONFIG_FS_DAX_PMD case?
    If it compiles fine we can just rely on IS_ENABLED() based dead code
    elimination entirely.

    > + /* if we are reading UNWRITTEN and HOLE, return a hole. */
    > + if (!write &&
    > + (iomap->type == IOMAP_UNWRITTEN || iomap->type == IOMAP_HOLE)) {
    > + if (!pmd)
    > + return dax_load_hole(xas, mapping, &entry, vmf);
    > + else
    > + return dax_pmd_load_hole(xas, vmf, iomap, &entry);
    > + }
    > +
    > + if (iomap->type != IOMAP_MAPPED) {
    > + WARN_ON_ONCE(1);
    > + return VM_FAULT_SIGBUS;
    > + }

    Nit: I'd use a switch statement here for a clarity:

    switch (iomap->type) {
    case IOMAP_MAPPED:
    break;
    case IOMAP_UNWRITTEN:
    case IOMAP_HOLE:
    if (!write) {
    if (!pmd)
    return dax_load_hole(xas, mapping, &entry, vmf);
    return dax_pmd_load_hole(xas, vmf, iomap, &entry);
    }
    break;
    default:
    WARN_ON_ONCE(1);
    return VM_FAULT_SIGBUS;
    }


    > + err = dax_iomap_pfn(iomap, pos, size, &pfn);
    > + if (err)
    > + goto error_fault;
    > +
    > + entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
    > + write && !sync);
    > +
    > + if (sync)
    > + return dax_fault_synchronous_pfnp(pfnp, pfn);
    > +
    > + ret = dax_fault_insert_pfn(vmf, pfn, pmd, write);
    > +
    > +error_fault:
    > + if (err)
    > + ret = dax_fault_return(err);
    > +
    > + return ret;

    It seems like the only place that sets err is the dax_iomap_pfn case
    above. So I'd move the dax_fault_return there, which then allows a direct
    return for everyone else, including the open coded version of
    dax_fault_insert_pfn.

    I really like where this is going!

    \
     
     \ /
      Last update: 2021-03-03 17:10    [W:3.586 / U:0.040 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site