Re: [Qemu-devel] [PATCH v6 08/33] exec: allow memory to be allocated from any kind of path

[Xiao Guangrong]

On 10/30/2015 10:04 PM, Vladimir Sementsov-Ogievskiy wrote:
> On 30.10.2015 08:56, Xiao Guangrong wrote:
> > Currently file_ram_alloc() is designed for hugetlbfs, however, the memory
> > of nvdimm can come from either raw pmem device eg, /dev/pmem, or the file
> > locates at DAX enabled filesystem
> >
> > So this patch let it work on any kind of path
> >
> > Signed-off-by: Xiao Guangrong <address@hidden>
> > ---
> >   exec.c | 56 +++++++++++++++++---------------------------------------
> >   1 file changed, 17 insertions(+), 39 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index 8af2570..3ca7e50 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -1174,32 +1174,6 @@ void qemu_mutex_unlock_ramlist(void)
> >   }
> >   #ifdef __linux__
> > -
> > -#include <sys/vfs.h>
> > -
> > -#define HUGETLBFS_MAGIC       0x958458f6
> > -
> > -static long gethugepagesize(const char *path, Error **errp)
> > -{
> > -    struct statfs fs;
> > -    int ret;
> > -
> > -    do {
> > -        ret = statfs(path, &fs);
> > -    } while (ret != 0 && errno == EINTR);
> > -
> > -    if (ret != 0) {
> > -        error_setg_errno(errp, errno, "failed to get page size of file %s",
> > -                         path);
> > -        return 0;
> > -    }
> > -
> > -    if (fs.f_type != HUGETLBFS_MAGIC)
> > -        fprintf(stderr, "Warning: path not on HugeTLBFS: %s\n", path);
> > -
> > -    return fs.f_bsize;
> > -}
> > -
> >   static void *file_ram_alloc(RAMBlock *block,
> >                               ram_addr_t memory,
> >                               const char *path,
> > @@ -1210,20 +1184,24 @@ static void *file_ram_alloc(RAMBlock *block,
> >       char *c;
> >       void *area;
> >       int fd;
> > -    uint64_t hpagesize;
> > -    Error *local_err = NULL;
> > +    uint64_t pagesize;
> > -    hpagesize = gethugepagesize(path, &local_err);
> > -    if (local_err) {
> > -        error_propagate(errp, local_err);
> > +    pagesize = qemu_file_get_page_size(path);
> > +    if (!pagesize) {
> > +        error_setg(errp, "can't get page size for %s", path);
> >           goto error;
> >       }
> > -    block->mr->align = hpagesize;
> > -    if (memory < hpagesize) {
> > +    if (pagesize == getpagesize()) {
> > +        fprintf(stderr, "Memory is not allocated from HugeTlbfs.\n");
> > +    }
>
> It is strange to see this warning every time.
>
> Shouldn't the differentiation be done explicitly in command line? May be 
> separate option mem-tlb, or
> separate flag tlbfs=on, or for new feature - new option mem-file, or prefixes 
> for paths (tlbfs://,
> file://).. Or the other way to not mix things but split them.

This is just a reminder to users. Currently Qemu do not stop user to append a 
regular file
for its backend memory, particularly, hugetlbfs is not the only way to use 
HugePage for
the THP-enabled system.

We can implement your idea as a independent patchset in the future.