rdmacg_try_charge(9)

💅 rdmacg_try_charge — the kernel API manual, bestie edition ✨

okay so bestie, we're looking at the kernel API manual page for rdmacg_try_charge, and honestly? it's giving resource-accounting main character energy. let's get into it 🎀

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🌸 NAME 🌸

rdmacg_try_charge — hierarchically try to charge the rdma resource. that's it, that's the vibe. it tries to charge. hierarchically. periodt 💅

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✨ SYNOPSIS ✨

int rdmacg_try_charge (struct rdma_cgroup **rdmacg , struct
       rdmacg_device *device , enum rdmacg_resource_type index );

look at that signature. so clean. so iconic. three args, one int coming back at you 🫶

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🦋 ARGUMENTS 🦋

• rdmacg — pointer to the rdma cgroup that's gonna own this resource. like, it's literally the new parent of your charge, no cap 👑
• device — pointer to your rdmacg device. the device in question. the one doing the thing 🎀
• index — index of the resource you wanna charge inside the cgroup (the resource pool, iykyk) ⭐

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🔥 DESCRIPTION 🔥

so here's the tea, bestie. this function follows the charging of a resource in a hierarchical way. it will fail if the charge would cause the new value to exceed the hierarchical limit — like, it's not gonna let you blow past the ceiling, that's not the move 🙈

it returns 0 if the charge succeeded; otherwise it gives you -EAGAIN, -ENOMEM, or -EINVAL. and when charging is successful, it returns a pointer to rdmacg for this resource. cute, right? ✨

now, the charger needs to account resources on two criteria, and yes you have to care about both:

• (a) per cgroup — the per-cgroup resource usage makes sure that tasks of the cgroup don't cross the configured limits 🚧
• (b) per device — resource usage. per device gives you granular configuration in multi-device usage, which is honestly highkey useful 🌈

it allocates a resource pool in the hierarchy for each parent it comes across, for the first resource. later on, that resource pool will be available — so it's gonna be much faster thereupon to charge/uncharge. the way that it just caches and slays 😭💖

ngl, the first pass is the expensive one. after that? smooth sailing, bestie. don't @ me, that's literally what the manpage says 💀

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👑 SEE ALSO 👑

• Kernel file ./kernel/cgroup/rdma.c
• uncharge_cg_locked(9)
• rdmacg_event_locked(9)
• rdmacg_uncharge_hierarchy(9)
• rdmacg_uncharge(9)
• rdmacg_register_device(9)
• rdmacg_unregister_device(9)
• rdmacg_css_offline(9)

go read those too, bestie, they're all in the group chat 🧚

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and that's the whole page! 🌟 this lil beauty lives under ./kernel/cgroup and it's dated October 2026, all under the rdmacg_try_charge(9) banner. mwah, go charge some rdma resources responsibly 💜💅