On Tue, 2008-12-16 at 13:54 -0800, Mike Waychison wrote: > Oren Laadan wrote: > > diff --git a/checkpoint/sys.c b/checkpoint/sys.c > > index 375129c..bd14ef9 100644 > > --- a/checkpoint/sys.c > > +++ b/checkpoint/sys.c > > > +/* > > + * During checkpoint and restart the code writes outs/reads in data > > + * to/from the checkpoint image from/to a temporary buffer (ctx->hbuf). > > + * Because operations can be nested, use cr_hbuf_get() to reserve space > > + * in the buffer, then cr_hbuf_put() when you no longer need that space. > > + */ > > This seems a bit over-kill for buffer management no? The only large > header seems to be cr_hdr_head and the blowup comes from utsinfo string > data (which could easily be moved out to be in it's own CR_HDR_STRING > blocks). > > Wouldn't it be easier to use stack-local storage than balancing the > cr_hbuf_get/put routines? I've asked the same question, so I'll give you Oren's response that I remember: cr_hbuf_get/put() are more of an API that we can use later. For now, those buffers really are temporary. But, in a case where we want to do a really fast checkpoint (to reduce "downtime" during the checkpoint) we store the image entirely in kernel memory to be written out later. In that case, cr_hbuf_put() stops doing anything at all because we keep the memory around. cr_hbuf_get() becomes, "I need some memory to write some checkpointy things into". cr_hbuf_put() becomes, "I'm done with this for now, only keep it if someone else needs it." This might all be a lot clearer if we just kept some more explicit accounting around about who is using the objects. Something like: struct cr_buf { struct kref ref; int size; char buf[0]; }; /* replaces cr_hbuf_get() */ struct cr_buf *alloc_cr_buf(int size, gfp_t flags) { struct cr_buf *buf; buf = kmalloc(sizeof(cr_buf) + size, flags); if (!buf) return NULL; buf->ref = 1; /* or whatever */ buf->size = size; return buf; } int cr_kwrite(struct cr_buf *buf) { if (writing_checkpoint_now) { // or whatever this write call was... vfs_write(&buf->buf[0], buf->size); } else if (deferring_write) { kref_get(buf->kref); } } -- Dave _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers