On Sep 27, 2021, at 2:24 AM, David Hildenbrand <david@xxxxxxxxxx> wrote:
On 26.09.21 18:12, Nadav Amit wrote:
From: Nadav Amit <namit@xxxxxxxxxx>
The goal of these patches is to add support for
process_madvise(MADV_DONTNEED). Yet, in the process some (arguably)
useful cleanups, a bug fix and performance enhancements are performed.
The patches try to consolidate the logic across different behaviors, and
to a certain extent overlap/conflict with an outstanding patch that does
something similar . This consolidation however is mostly orthogonal
to the aforementioned one and done in order to clarify what is done in
respect to locks and TLB for each behavior and to batch these operations
more efficiently on process_madvise().
process_madvise(MADV_DONTNEED) is useful for two reasons: (a) it allows
userfaultfd monitors to unmap memory from monitored processes; and (b)
it is more efficient than madvise() since it is vectored and batches TLB
flushes more aggressively.
MADV_DONTNEED on MAP_PRIVATE memory is a target-visible operation; this is very different to all the other process_madvise() calls we allow, which are merely hints, but the target cannot be broken . I don't think this is acceptable.
This is a fair point, which I expected, but did not address properly.
I guess an additional capability, such as CAP_SYS_PTRACE needs to be
required in this case. Would that ease your mind?