Messages in this thread | | | From | Christoph Rohland <> | Subject | Re: pte-highmem-5 | Date | Thu, 17 Jan 2002 17:11:48 +0100 |
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Hi Andrea,
On Thu, 17 Jan 2002, Andrea Arcangeli wrote: > (btw, I suspect allocating one page at offset 4G in every shmfs file > could make the overhead per page of shm to increase)
Nearly: A sparse file with the only page at 4G is the worst case: You need three extra pages to hold the swap entry. The ratio goes fown as soon as you add more pages somewhere.
> But in real life I really don't expect problems here, one left page > of the vector holds 1024 swap entries, so the overhead is of the > order of 1/1000. On the top of my head (without any precise > calculation) 64G of shm would generate stuff of the order of some > houndred mbytes of ram
Ok, 64GB shm allocate roughly 64MB swap entries, so this case should not bother too much. I was still at the 390x case where we have 512 entries per page. But they do not need highmem.
Another case are smaller machines with big tmpfs instances: They get killed by the swap entries. But you cannot hinder that without swapping the swap entries themselves.
Greetings Christoph
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