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call fadvise DONTNEED for the byterange we actually have read, fixes #158 

avoid throwing away potential readahead data the OS might have read into the cache.
This commit is contained in:
Thomas Waldmann 2015-08-20 05:33:51 +02:00
parent 0926c2821f
commit d3d78f7ae3
1 changed files with 8 additions and 3 deletions
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11
borg/_chunker.c
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@ -128,6 +128,7 @@ static int
chunker_fill(Chunker *c)
{
ssize_t n;
size_t offset, length;
PyObject *data;
memmove(c->data, c->data + c->last, c->position + c->remaining - c->last);
c->position -= c->last;
@ -137,6 +138,7 @@ chunker_fill(Chunker *c)
return 1;
}
if(c->fh >= 0) {
offset = c->bytes_read;
// if we have a os-level file descriptor, use os-level API
n = read(c->fh, c->data + c->position + c->remaining, n);
if(n > 0) {
@ -151,13 +153,16 @@ chunker_fill(Chunker *c)
// some error happened
return 0;
}
length = c->bytes_read - offset;
#if ( _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L )
// We tell the OS that we do not need the data of this file any more
// that it maybe has in the cache. This avoids that we spoil the
// We tell the OS that we do not need the data that we just have read any
// more (that it maybe has in the cache). This avoids that we spoil the
// complete cache with data that we only read once and (due to cache
// size limit) kick out data from the cache that might be still useful
// for the OS or other processes.
posix_fadvise(c->fh, (off_t) 0, (off_t) 0, POSIX_FADV_DONTNEED);
if (length > 0) {
posix_fadvise(c->fh, (off_t) offset, (off_t) length, POSIX_FADV_DONTNEED);
}
#endif
}
else {