VirtualAllocEx function (Windows)
I don't believe relationships fail. Research into the science of love clearly shows that love is about growth. However, over time you can stagnate. And, as a bonus, system memory-lists and VirtualAlloc calls for all . defined by where the allocation time and free time occur in relation to the. A breakup can send you spiraling downward, reviving old thought patterns and collecting negative beliefs about yourself. Or it can be the.
I'd guess it's a side effect of XFS's focus on performance and code quality. As a high-performance filesystem, it puts more stress on the VM subsystem. And as for code quality, there's a reason why the filesystem testing tool every filesystem uses is called "xfstests".
The "too small to fail" memory-allocation rule Posted Dec 24, 5: If you're comparing XFS to vfat or ext3, remember that those are really simple filesystems. Almost everything is in fixed-size arrays or bitmaps, and disk blocks have a 1: Not much interesting for MM to do. Comparing XFS to btrfs: To do this, we have to have some idea of how the MM subsystem works, how it is architected, the rules we have to play under, the capabilities and deficiencies it has, etc.
Just because we work on filesystems doesn't mean we only understand filesystems Further, most XFS developers come from a strong engineering background where we are taught to understand and solve the root cause of whatever issue is occurring, not just slap a band-aid over the symptom being reported. Hence you see us pointing out warts in other parts of the system that haven't been well thought out, work around some issue or are just plain broken.
This thread was a prime example - "XFS deadlocked under low memory conditions" was the bug report, but a little bit of investigation of the report points out the underlying cause of the hang is not a filesystem problem at all If I understood it correctly, the problem is a "recursive locking" deadlock: Couldn't the meaning of that flag be extended to also mean "don't wait for the OOM killer even for small allocations", since filesystem and memory management code have a higher probability of having a good quality error recovery code?
The "too small to fail" memory-allocation rule Posted Dec 24, 3: Such an allocation must not risk waiting for FS or IO activity. Yet waiting for the OOM killer can clearly do that. This is a violation of the interface whether you accept the "too small to fail" rule or not. Invoking the OOM killer is reasonable, waiting a little while is reasonable, but waiting for the killed processes to flush data or close files is not This is set on a thread when it has been chosen to die.
Looking at the original patch which started this: So no memory will become available, so it will stay stuck in the filesystem Then another process can be killed even if the first one blocked But that analysis was very hasty and probably misses something important. The "too small to fail" memory-allocation rule Posted Jan 15, First, the allocator is at all called with a lock held, implying that allocation length follows from state which the lock is used to guard; which in turn implies overly eager design.
Second, that the allocator enters the OOM killer on its own volition, changing malloc's locking behaviour from "only ever the heap lock" to "everything an asynchronous OOM killer might end up with".
That might well cover all of the kernel, when the caller is expecting malloc to be atomic by itself.
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What's surprising isn't so much the reams of untested malloc-failure handling code, but that this bug comes up as late as Then, it should have local management of its own resources. It could have optional dynamic reservation for non-critical purposes, such as caching, where it doesn't matter if the data is dropped only a performance impact. The "too small to fail" memory-allocation rule Posted Dec 24, 0: Sufficient memory should be allocated in advance, so you can always close files etc without allocating.
The "too small to fail" memory-allocation rule Posted Dec 24, 4: I wonder this too, and have done so for as long as the OOM killer has existed. It seems that instead of returning ENOMEM or calling panicwe've decided that inflicting a Chaos Monkey on userspace and adding a bunch of latency for the allocating process is somehow the best of all feasible alternatives. For example, Linux allows to fork a process even if its image has more then halve the memory on the system.
Now consider what should happen when the processes start to write to the memory. That may lead to OOM errors. Now, who should be blamed for it? The child or parent? In addition, applications are typically not prepared to deal with a situation when an arbitrary write may trigger OOM. So OOM killer is pretty reasonable solution. Compare that with Windows where overcommit is not available lack of fork in Windows API allows for that.
Immediately memory accounting becomes simple and OS can guarantee that if a process has a pointer to writable memory, then memory is always available for writing. The "too small to fail" memory-allocation rule Posted Dec 24, 9: Remembering that 'things should be as simple as possible, but no simpler', it is just a bit too simple. POSIX does define spawn functions which userspace code might call instead.
The "too small to fail" memory-allocation rule [relax-sakura.info]
Essentially, when you fork the kernel has no way of knowing that you are just about to call exec immediately afterwards, so it has to either reserve space for a complete copy of all your process's memory, or end up overcommitting and resorting to an OOM killer if it guessed wrong. If userland can give the kernel a bit more information then the kernel can do its job better. It's easy to do this in a race-free way.
Also, copy-on-write fork ing has other valuable uses. In rr we use it to create checkpoints very efficiently.
But the manipulation of file descriptors shouldn't require a complete copy of the parent process's memory. It would be handy if you could fork passing a buffer of memory and a function pointer. The child process will be given a copy of that buffer and will jump to the function given. Then you have some flexibility in what you can do before exec but you can still be frugal in memory usage without relying on overcommit.
The "child" shares memory with the parent until it calls exec, so you avoid not only the commit charge catastrophe of copy-on-write fork, but also gain a significant performance boost from not having to copy the page tables. The conjecture so far is that there is a problem, since a forked process gets a copy of its parent's address space, which requires either reserving enough memory RAM or swap to provide that, or else overcommitting and crossing your fingers with OOM killer for when you get it wrong.
It is true that copy-on-write means the kernel doesn't have to copy all the pages straight away, but that is just a time saving; it doesn't resolve the underlying issue of needing overcommit. But it has other limitations. Compare that with, say, FreeBSD or Solaris that, according to the manual pages, suspends the whole parent process during the vfork call. The "too small to fail" memory-allocation rule Posted Dec 30, 0: Safe, okay, but not really efficient. Makes it all rather non portable though.
Although, as documented, Windows does always reserve the whole size of the memory region in the pagefile. The penalty for actually using the memory then becomes swapping rather than random process death. Many programs like the JVM reserve large chunks of address space on startup and internally allocate out of that. That means that programs written by the few well-intentioned developers are aware of overcommit issues frequently don't end up working correctly.
All this gives mmap 2 a Rusty Russel score of around The manual page talks about error reporting through SIGSEGV, which should be sufficiently discouraging to anyone who actually reads it. Do not reserve swap space for this mapping. When swap space is reserved, one has the guarantee that it is possible to modify the mapping. If you understand this two-step dance then you will now know how to use it.
You need to set the Heap-profiled process name and select Heap tracing to file before launching the process that you want to trace. And you need to start tracing before any data will actually be recorded. Whether you start tracing before or after you start your process es determines whether or not you will record allocations made at process startup. And yes, this does work for multiple processes.
When I profile Chrome I get heap data from all Chrome processes — as long as they are started after the registry key is set. It even works for multiple different process names. In the UIforETW settings dialog type in one or two PIDs, separated by semi-colons, then set the heap tracing type to Heap tracing to file and when you start tracing you will get heap data from the processes specified. To use this method you need to put a fully qualified path to the binary to launch in the heap-profiled processes field.
Then when you start heap tracing this executable will be launched and traced. Analyzing heap traces After you have recorded your scenario keep it short to avoid generating traces that are large and unwieldy you save the trace buffers as usual.
The UIforETW startup profile does not initially show any graphs for viewing heap or memory data so you will need to add them and optionally save a new startup profile.
The memory graphs are surprise! If you drag this over you will get the WPA default settings for viewing the heap which, as usual, I think are wrong. The default view shows columns that are usually not needed such as Address and AllocTime, and omits vital columns such as Stack and Type.
Now you can start drilling down into your process or processes. If you want to group by heap you can add the Handle column but it is usually of minimal interest. The next column is the most crucial and least obvious. In the world of ETW memory explorations there are four Types of allocations, defined by where the allocation time and free time occur in relation to the displayed timespan.
These are blocks of memory that were allocated in the displayed timespan but were not freed in the displayed timespan. These are the most important type of allocations if you are looking for memory consumed in a time region. They may have been freed after the displayed timespan, or never. Once you understand why, you can find more positive ways to achieve the same end. A single betrayal--or an act perceived as a betrayal--can wipe out a lifetime of trust.
If trust is absent, again, ask why? Is it warranted, or is it coming from something unresolved in in a past relationship? If there has been a breach, is it too serious to be mended? If one or both partners is consistently tuning out, seeking distractions, and making a conscious effort to avoid making a connection, it may be that the bond between you has already been severed. People check out for all kinds of reasons--some temporary, others permanent. It's not unusual to respond defensively when you're challenged.
Over time, defensiveness shifts into the "whatever" stage, which throws up a protective isolating barrier. Wherever the need for this protective stance originates, it prevents open communication and a meaningful relationship. The most serious possible sign; once a relationship is at this point, the odds of survival are low.
It's often a way of turning one's own despised and unwanted feelings outward, so left alone it may recur in later relationships as well.