[PATCH] debuginfo fdcache prefetching tweak

Mark Wielaard mark@klomp.org
Wed Oct 21 12:43:53 GMT 2020


Hi Frank,

On Tue, 2020-10-20 at 20:45 -0400, Frank Ch. Eigler via Elfutils-devel wrote:
> Subject: [PATCH 2/2] debuginfod: suppress fdcache prefetching during dwz
>  lookup
> 
> From: Frank Ch. Eigler <fche@redhat.com>
> 
> During a recent from-scratch reindexing of the rpm/deb corpus at
> debuginfod.elfutils.org, we found the fdcache chewed up an abnormal
> amount of $TMPDIR space.  This was due to internal .dwz lookups, which
> triggered fdcache prefetching as for a webapi query, but there was not
> a timely fdcache eviction pass to clean it up again.  Rather than add
> that pass, it's better to suppress the prefetching completely, as an
> internal .dwz search will only ever need that file, not any others
> from the same archive.

Makes sense. Only one comment:

>  static struct MHD_Response*
> -handle_buildid_r_match (int64_t b_mtime,
> +handle_buildid_r_match (bool internal_req_p,
> +                        int64_t b_mtime,
>                          const string& b_source0,
>                          const string& b_source1,
>                          int *result_fd)
> @@ -1358,7 +1361,8 @@ handle_buildid_r_match (int64_t b_mtime,
>    // 3) extract some number of prefetched entries (just into fdcache)
>    // 4) abort any further processing
>    struct MHD_Response* r = 0;                 // will set in stage 2
> -  unsigned prefetch_count = fdcache_prefetch; // will decrement in stage 3
> +  unsigned prefetch_count =
> +    internal_req_p ? 0 : fdcache_prefetch;    // will decrement in stage 3
>  
>    while(r == 0 || prefetch_count > 0) // stage 1, 2, or 3
>      {

So we still setup the whole archive, but then don't actually iterate
through it. So shouldn't we check internal_req_p a little earlier and
just return from handle_buildid_r_match when it is set and we hit "no
match ... grumble, must process the archive"?

Cheers,

Mark


More information about the Elfutils-devel mailing list