vdr uses quite a lot of memory, RSS here used to be ~70M, so i decided to see
if it could be
reduced a bit. First suspects became the ringbuffers, cause i was seeing a lot
of log lines
such as buffer stats: 96068 (1%) used. Turns out many buffers are way over
sized, only a few
percent of the memory are typically used, yet because of how a ringbuffer works
_all_ of it is
constantly accessed. I first tried to make the ringbuffer users smarter about
picking the size
and eg after changing the transfer buffer to start out small and use bigger
sizes only when the
current one isn't large enough it seemed a more reasonable size for that vdr
instance was 384k
instead of 2M. Similarly the TS buffer could be just a few hundred K instead of
2M.
But that approach was not ideal as there isn't anything one could do after
realizing the buffer
is too small, it could be grown next time, after channel switch etc, but that's
it. Also some
of the huge buffers came from plugins, and I wasn't all that excited about
fixing all of them
(one example w/ the one-digit % fill was streamdev-server).
It is hard to estimate what the proper size would be under load, with many
simultaneous recordings.
So I did attack this issue differently -- by making the ringbuffers themselves
smarter.
Patch below changes the interpretation of the 'Size' parm given when creating a
buffer from a
fixed length to a max limit. The buffers start out much smaller (currently
128k, instead of many
megabytes) and grow automatically when they become almost full. This way all
callers benefit,
and they don't have to be modified at all.
The buffers are actually always allocated using the max size, but only the
necessary
buffer part is used, the rest of the memory is never accessed; this is done
this way
so that no extra locking is necessary.
I've tested this on two vdrs for a few hours and it seems to work, but it needs
a lot
more testing.
There is some extra logging in this patch so that you can see what's going on;
every
time a ring buffer gets deleted it logs a line which tells you exactly how much
memory
was requested and how much was really needed.
vdr: [19729] Deleting ring buffer TS size: 196608 / 2097152 (used 9.375% of
requested size)
vdr: [19718] Deleting ring buffer Result size: 262144 / 262144 (used 100% of
requested size)
vdr: [19718] Deleting ring buffer Recorder size: 442368 / 5242880 (used
8.4375% of requested size)
vdr: [19718] Deleting ring buffer Result size: 262144 / 262144 (used 100% of
requested size)
vdr: [19718] Deleting ring buffer Recorder size: 131072 / 5242880 (used 2.5%
of requested size)
vdr: [19733] Deleting ring buffer TS size: 131072 / 2097152 (used 6.25% of
requested size)
vdr: [19718] Deleting ring buffer Result size: 262144 / 262144 (used 100% of
requested size)
vdr: [19718] Deleting ring buffer Recorder size: 442368 / 5242880 (used
8.4375% of requested size)
So each of the several 'Recorder' buffers was an order of magnitude smaller
than w/o
this patch and several megabytes less ram was used.
artur
diff --git a/ringbuffer.c b/ringbuffer.c
index 0633bd3..8dd1efe 100644
--- a/ringbuffer.c
+++ b/ringbuffer.c
@@ -151,13 +151,29 @@ void cRingBufferLinear::PrintDebugRBL(void)
}
#endif
+// cRingBufferLinear are dynamically sized, or at least we can pretend they
are ;)
+// We treat 'Size' as the maximum size, but start with a small buffer, which
can
+// grow later as it fills up. Memory is always allocated for the full buffer,
but
+// the unused RAM portion remains untouched until (if at all) it is actually
needed.
+// Note that we can not start with a larger than requested buffer because
there are
+// ring buffer users that cause crashes then (eg softdevice mpegdecoder
absolutely
+// needs 32/64k).
+
+// Startup size. 64k still causes overflows before buffer starts to grow, 128k
doesn't.
+// The buffers grow to 200..500k anyway, so maybe increasing this a bit more
would
+// make sense, but let's first see if it's really needed.
+#define DEFRBSIZE KILOBYTE(128)
+
cRingBufferLinear::cRingBufferLinear(int Size, int Margin, bool Statistics,
const char *Description)
-:cRingBuffer(Size, Statistics)
+:cRingBuffer(min(Size,DEFRBSIZE), Statistics)
{
description = Description ? strdup(Description) : NULL;
tail = head = margin = Margin;
gotten = 0;
buffer = NULL;
+ maxsize = Size;
+ growbuf = 0;
+ dsyslog(New ring buffer \%s\ size: %d margin: %d, description, Size,
Margin );
if (Size 1) { // 'Size - 1' must not be 0!
if (Margin = Size / 2) {
buffer = MALLOC(uchar, Size);
@@ -183,6 +199,8 @@ cRingBufferLinear::~cRingBufferLinear()
#ifdef DEBUGRINGBUFFERS
DelDebugRBL(this);
#endif
+ dsyslog(Deleting ring buffer \%s\ size: %d / %d (used %g%% of requested
size), description,
+ size, maxsize,
size/(double)maxsize*100.0 );
free(buffer);
free(description);
}
@@ -207,6 +225,13 @@ void
